Redescription and reassessment of the phylogenetic affinities of Euhelopus zdanskyi (Dinosauria:...

Journal of Systematic Palaeontology 7 (2): 199–239 Issued 26 May 2009

doi:10.1017/S1477201908002691 Printed in the United Kingdom C© The Natural History Museum

Redescription and reassessment

of the phylogenetic affinities of

Euhelopus zdanskyi (Dinosauria:

Sauropoda) from the Early

Cretaceous of China

Jeffrey A. WilsonMuseum of Paleontology & Department of Geological Sciences, University of Michigan, 1109 GeddesAvenue, Ann Arbor, Michigan 48109–1079, USA

Paul UpchurchDepartment of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK

SYNOPSIS Euhelopus zdanskyi was the first dinosaur described from China. Both traditional andmodern cladistic assessments have found support for an endemic clade of Chinese sauropods (Eu-helopodidae) that originated during an interval of geographic isolation, but the monophyly of thisclade has remained controversial. The phylogenetic affinity of the eponymous genus Euhelopus iscentral to this controversy, yet its anatomy has not been completely restudied since the originalGerman-language monograph in 1929.

We jointly re-examined the cranial and postcranial anatomy of the holotypic and referred materi-als of Euhelopus to provide a new diagnosis for the genus and to explore its phylogenetic affinities.Diagnostic features of Euhelopus include: postaxial cervical vertebrae that have variably developedepipophyses and more subtle “pre-epipopophyses” below the prezygapophyses; cervical neuralarches with an epipophyseal–prezygapophyseal lamina separating two pneumatocoels; anterior cer-vical vertebrae with three costal spurs on the tuberculum and capitulum; divided middle presacralneural spines, which in anterior dorsal vertebrae bear a median tubercle that is as large or larger thanthe metapophyses; middle and posterior dorsal parapophyseal and diapophyseal laminae arrangedin a “K” configuration; and presacral pneumaticity that extends into the ilium. Following this mor-phological study, we rescored Euhelopus for the two most comprehensive sauropod data matrices(Wilson 2002; Upchurch et al. 2004a), which previously yielded vastly different hypotheses for its re-lationships. Both matrices decisively demonstrate that Euhelopus is closely related to Titanosauria;traditional and cladistic claims that Euhelopus, Omeisaurus, Mamenchisaurus and Shunosaurusformed a monophyletic “Euhelopodidae” endemic to East Asia are not supported. These resultssuggest that there were at least two clades of very long-necked sauropods in East Asia, occurringin the Middle Jurassic (i.e. Omeisaurus + Mamenchisaurus) and Early Cretaceous (e.g. Euhelopus,Erketu), with the latter group perhaps also occurring in Europe (Canudo et al. 2002). It is probablethat the Euhelopus + Erketu lineage invaded East Asia from another part of Pangaea when isolationended in the Early Cretaceous. The large number of basal titanosauriforms from East Asia has beeninterpreted to mean that this area may represent their centre of origin (You et al. 2003), but thetitanosaur fossil record and phylogenetic studies indicate that the group probably originated prior tothe Middle Jurassic and acquired a virtually global distribution before Pangaean fragmentation.

KEY WORDS palaeontology, Asia, phylogeny, sauropod, palaeobiogeography

Email: [email protected]: [email protected]

Contents

Introduction 200

Institutional abbreviations 201

Collection history 201Exemplar a 201Exemplar b 201Exemplar c 201

200 J . A. Wilson and P. Upchurch

Systematic History 202

Age of the Mengyin Formation 203

Systematic palaeontology 205Dinosauria Owen, 1841 205

Saurischia Seeley, 1887 205Sauropoda Marsh, 1878 205

Neosauropoda Bonaparte, 1986 205Titanosauriformes Salgado et al., 1997 205

Euhelopus Romer, 1956 205Euhelopus zdanskyi (Wiman 1929) 205

Description 206Skull 207Vertebral column 210Cervical vertebrae 211Cervical ribs 217Dorsal Vertebrae 218Dorsal ribs 221Sacral vertebrae 221Scapula, coracoid and humerus 222Pelvis 223Hindlimb 223

Discussion 227Phylogenetic affinities of Euhelopus 227Euhelopus and the biogeographical history of East Asian sauropods 229

Conclusion 233

Acknowledgements 235

References 235

Introduction

In contrast to the much longer history of dinosaur studiesin Europe (Plot 1677; Mantell 1825), North America (Leidy1858), India (Falconer 1868), Madagascar (Deperet 1896)and South America (Lydekker 1893), Asian dinosaurs firstappeared in the scientific literature in the 1920s with theCentral Asiatic Expedition’s discoveries in the Gobi Desert ofMongolia (Andrews 1932). A flurry of descriptions of now-famous dinosaurs followed, including the ceratopsians Pro-toceratops and Psittacosaurus, the ankylosaur Pinacosaurusand the theropods Oviraptor and Velociraptor (Granger &Gregory 1923; Osborn 1923, 1924a). In addition to this ex-cellent material, Osborn (1924b) also described much morefragmentary remains of the first sauropod from Asia, Asi-atosaurus mongoliensis, now considered a nomen dubium(McIntosh 1990; Barrett et al. 2002; Upchurch et al. 2004a).At the time of these descriptions, the Sino-Swedish Palaeon-tological expedition was concluding its long tenure in Asiawith the excavation of the sauropod Euhelopus zdanskyi, thefirst of many excellent sauropod skeletons to emerge fromChina (Wiman 1929; Mateer & Lucas 1985).

Despite this somewhat “late start”, Asian dinosaursnow represent 21.3% of all dinosaur discoveries (datadownloaded from the Paleobiology Database on 21 August2006, using the group name “vertebrate” and the following

parameters: time interval = Mesozoic, taxon = Dinosauria,region = Asia). Phylogenetic affinities of the Asian sauro-pod fauna suggest an interesting temporal pattern: whereasall Jurassic Asian sauropods fall outside the neosauropod ra-diation, nearly all Cretaceous Asian species belong to theneosauropod subgroup Titanosauriformes (Wilson 2005a).This pattern has been interpreted as the consequence of aninterval of geographical isolation lasting from Middle Jur-assic until Cretaceous times (Russell 1993; Upchurch 1995;Buffetaut & Suteethorn 1999; Luo 1999; Barrett et al. 2002;Upchurch et al. 2002; Zhou et al. 2003). If a physical bar-rier prevented neosauropods from dispersing into Asia, thenthis same barrier should have prevented basal sauropodsfrom leaving Asia, which would imply the emergence ofendemic clades. Euhelopodidae was forwarded as an exem-plary endemic Asian sauropod clade (Upchurch 1995, 1998;Upchurch et al. 2002), a grouping that remains a central con-troversy in sauropod systematics (Wilson & Sereno 1998;Wilson 2002; Upchurch et al. 2004a).

In this contribution, we test the monophyly of Euhel-opodidae following revision of the anatomy and diagnosisof its namesake species, Euhelopus zdanskyi. We begin byproviding an introduction to the history of discovery and thetaxonomy of Euhelopus, as well as the age of the MengyinFormation. Next, we redescribe the cranial and postcranialanatomy of Euhelopus, based on our joint examination of

Redescription and reassessment of Euhelopus zdanskyi 201

materials housed in the Palaeontological Museum ofUppsala, Sweden. This redescription forms the basis for thethird portion of our contribution, in which we rescore andreanalyze the data matrices of Wilson (2002) and Upchurchet al. (2004a), the two most recent global analyses of saur-opod genera. Finally, we explore the implications of thephylogenetic affinities of Euhelopus for Cretaceous Asianpalaeobiogeography.

Institutional abbreviations

BMNH = British Museum (Natural History), London, UKIGM = Geological Institute of the Mongolian Academy

of Sciences, Ulaan Baatar, MongoliaMB = Museum fur Naturkunde der Humbolt-

Universitat, Berlin, GermanyPMU = Palaeontological Museum, Uppsala, Sweden.

Collection history

Euhelopus zdanskyi is known from two specimens that werecollected from grey sandstone deposits from the MengyinValley of central Shandong Province, northeastern China(Fig. 1) on three different occasions by three different parties.Wiman (1929:5) reported that the initial discovery of a dino-saur in Mengyin was made by a Father R. Mertens in 1913.Around 1916, some bones from Mertens’ specimen weregiven to Dr V. K. Ting, Director of the Geological Surveyof China, by German mining engineer W. Behegel (Young1935). These were probably the first dinosaur remains acces-sioned to a modern repository in China, although fossils ingeneral, and dinosaurs in particular, were known to ancientChinese scholars (Needham 1956; Mayor 2000). The proven-ance of Mertens’ skeleton was unknown for some time, untilChinese geologist C. H. Tan and Sino-Swedish Expeditionleader J. G. Andersson relocated the site in November 1922(Wiman 1929:5; Mateer & Lucas 1985:15). The majority ofEuhelopus material was discovered and excavated later fromthis locality. In March 1923, Otto Zdansky collected twopartial sauropod skeletons, referred to as “exemplar a” and“exemplar b”. These specimens are housed in the Palaeonto-logical Museum of Uppsala under accession numbers PMU233 and PMU 234, respectively. Zdansky (pers. comm. inMateer & McIntosh 1985:125) was forced to forgo com-plete excavation of exemplar a because he was obliged toreturn to Beijing, and Wiman (1929:7) remarked: “There areprobably parts of this skeleton [exemplar a] somewhere else,but since they have apparently been ruined during excav-ation, I did not intend to fit them in” [translated from theGerman by J.A.W.]. A decade later, Chinese palaeontologistC. C. Young and geologist N. Bien returned to Zdansky’squarry in Autumn 1934 and collected additional materialthat probably pertains to exemplar a. We provisionally referto this material as “exemplar c”. Its whereabouts are currentlyunknown.

Exemplar a

Wiman (1929:7) reported that Zdansky collected exemplara (PMU 233) 40 li northwest of Mengyin and 2 li west of

Figure 1 Map of China showing the position of the Euhelopuslocality (bulls-eye) and map showing the position of Asia during theEarly Cretaceous (120 Ma; modified from Blakey 2006). The map is aMollweide projection with latitude and longitude lines spaced at 30◦

intervals.

“Ning Chia Kou” (now Ningchiakou) in Yantai County ofShandong Province, which juts into the Bohai and YellowSeas (Fig. 1). A “li” is a traditional Chinese unit of meas-urement that at the time of Wiman’s writing was equivalentto 608.7 yards or 556.6 m (Alexander 1857). Based on thisconversion, exemplar a was collected approximately 22 kmnortheast of Mengyin and approximately 1 km west of Ning-chiakou. Exemplar a consists of a partial skull and lowerjaws, an articulated vertebral series from the axis to the 25thpresacral, a dorsal rib and a left femur (Fig. 2). The vertebralseries appears to be continued by a series of articulated dorsalvertebrae described by Young (1935) from the same quarry(exemplar c; see below).

Exemplar b

The partial skeleton of exemplar b (PMU 234) was collectedapproximately 2–3 km from exemplar a (Wiman 1929), butthe relative positions of the sites are not known. Exemplarb consists of a series of articulated dorsal and sacral verteb-rae, two dorsal ribs, pelvis and left hindlimb lacking somephalanges (Fig. 2). Only the femur and posterior dorsal ver-tebrae overlap with exemplar a. The strong resemblance inoverall morphology and the presence of a crisscross patternof “K” laminae (see Description, below) on the lateral as-pect of the posterior dorsal neural arches clearly indicate thatexemplar b is referable to E. zdanskyi.

Exemplar c

As noted above, Wiman (1929) left open the possibility thatadditional bones remained at the exemplar a locality. Young


Figure 2 Schematic representation of preserved elements of the holotype (top) and referred specimen (bottom) of Euhelopus zdanskyi.Skeletal outlines are shown in right lateral view, and light grey tone indicates limb elements from the left side. Exemplar c is considered to bepart of the holotype (see the text and Fig. 3). Holotypic and referred skeletons of Euhelopus overlap in the middle dorsal region and in the femur,and autapomorphies in the dorsal vertebrae (see the text) support referral of exemplar b to Euhelopus zdanskyi.

and Bien returned to the area 11 years after Zdansky andcollected a left scapula, coracoid and humerus. In the paperdescribing these forelimb remains, Young (1935:523) alsodescribed the partial series of vertebrae “sent to Dr. V. K.Ting by Behagel”, which “probably are also a part of . . . theskeleton a of Uppsala”. The adjoining portions of the dorsalseries collected by Behagel and exemplar a of Wiman ap-pear to fit – the first-preserved of Young’s series is a pos-terior portion of a vertebra that is broken obliquely from thepostzygapophyses to the anterior neural arch pedicle, andthe last-preserved vertebra of Wiman’s exemplar a is brokenobliquely from the postzygapophyses forward to the anteriorcentrum (Fig. 3). Although we were not able to examine thesevertebrae because their location is not known, we believethat they belong to exemplar a. Young’s (1935:523) conten-tion that the limb material that he and Bien collected alsopertains to exemplar a is less well supported but certainlyplausible. The remains were collected at or nearly at the samelocality as exemplar a, there is no duplication of elementsbetween the two specimens, and the size of the elements isconsistent. Exemplar c includes a series of four dorsal verteb-rae, as well as a left scapula, left coracoid, and a left humerus

(Fig. 2). We consider it highly probable that exemplars a andc pertain to the same individual, but we retain separate namesfor them in the discussion that follows.

Young and Bien also purchased a right coracoid collec-ted by a villager somewhere near Ningchiakou, but the exactlocality is not known (Young 1935:528). They ascribed thiselement to a sauropod, but it is quite narrow transversely andprobably pertains to a large theropod dinosaur. We also notethat the supposed theropod ulna collected from the nearbylocality of “Hsichufu” (Young 1935:fig. 8) is actually a prox-imal fragment of a pterosaur wing phalanx 1 (ph IV.1).

Systematic history

The original generic name Helopus means “marsh-foot” andrefers to the sauropod pes, which Wiman (1929: fig. 2)likened to trugors, a “kind of snowshoe used in the North ofSweden both by horses and by men for walking on marshesor loose snow” (Save-Soderbergh 1946:401). At the time ofWiman’s writing, no hierarchical structure existed in sauro-pod taxonomy, which consisted of 5–6 families erected by


Figure 3 Comparison of posteriormost preserved presacralvertebrae of exemplar a (Wiman 1929: pl. 3) and the anteriormostpreserved presacral vertebrae of exemplar c, which was described byYoung (1935: fig. 1).

Marsh (1882, 1895). Although Janensch’s (1929) dichotom-ous scheme for sauropod taxonomy, which divided sauropodsinto the broad-crowned group Bothrosauropodidae and thenarrow-crowned group Homalosauropodidae, appeared thatsame year, it was not popularised until Huene (1956) andRomer (1956) adopted it (Wilson & Sereno 1998; Wilson2005b). Consequently, Wiman (1929:28–29) presented a re-latively limited discussion of the taxonomy of “Helopus”,allocating it to its own Subfamily Helopodinae within “Car-diodontidae” (= Cetiosauridae; Table 1).

The second sauropod described from China, Tien-shanosaurus, was assigned to Helopodinae by Young(1937:21), who placed the subfamily within Morosauridae(= Camarasauridae). Shortly thereafter, Young (1939) namedOmeisaurus and also included it in Helopodinae, which hethen regarded as a subfamily of Brachiosauridae – presum-ably because of the long neck shared by members of thegroup. Romer (1956:621) followed Young’s taxonomic ar-rangement but changed the name of the genus and subfam-ily to Euhelopus and Euhelopodinae, respectively, because“Helopus” had been coined well over a century earlier byWagler (1832) for the Caspian Tern, which itself was latersynonymised with Hydroprogne caspia.

The fourth Chinese sauropod, Mamenchisaurus, wasdescribed by Young (1954) with little taxonomic discussion,but the description of a more complete skeleton was ac-companied by a classification of Chinese sauropods (Young1958). By this time, Janensch’s dichotomy had been popular-ised by Huene (1956) and Romer (1956). Young (1958:25)considered Mamenchisaurus distinct at the suprafamiliallevel from earlier-named genera and placed it in the narrow-crowned group Homalosauropodidae (Table 1). Young &Zhao (1972) maintained the split of Asian sauropods into

broad-crowned and narrow-crowned groups, but separatedEuhelopus – rather than Mamenchisaurus – from the otherthree genera, which were now regarded as members ofthe narrow-crowned subgroup Homalosauropodidae. At thispoint, dental material was available only for Euhelopus,which was clearly broad-crowned. Bonaparte (1986) andMcIntosh (1990) provided the last “traditional” sauropodclassifications. Bonaparte ignored Chinese sauropods in his1986 discussion of the phylogenetic relationships of Jur-assic sauropods and in his 1999 treatise on the vertebralanatomy of sauropod dinosaurs, but McIntosh (1990) clas-sified all major Chinese sauropods, favouring their sep-aration amongst the Families Cetiosauridae (Shunosaurus,Omeisaurus), Camarasauridae (Euhelopus) and Diplodo-cidae (Mamenchisaurus).

Cladistic assessments of the phylogenetic affinities ofthe Chinese sauropods are split between the view that theyform a monophyletic group of euhelopodid sauropods andthe view that they are a paraphyletic assemblage of basaland derived forms (Fig. 4). Analyses by Upchurch (1995,1998) gave cladistic valence to the view of Young and oth-ers that the Chinese sauropods Shunosaurus, Omeisaurus,Mamenchisaurus and Euhelopus form a natural group calledEuhelopodidae (Table 1). In these two analyses, Upchurchpresented character evidence that (1) supported euhelopo-did monophyly and (2) excluded euhelopodids from mem-bership in Neosauropoda. Wilson & Sereno (1998) andWilson (2002) presented an alternative view that thesefour Chinese genera form a paraphyletic series includ-ing non-neosauropods (Shunosaurus, Omeisaurus + Ma-menchisaurus) and one neosauropod closely related to titano-saurs (Euhelopus). Finally, Upchurch et al. (2004a) presentedan analysis of genus-level sauropod relationships that did notrecover a monophyletic Euhelopodidae. Although still posi-tioned outside Neosauropoda, the four Chinese genera wereresolved as a paraphyletic series.

Age of the mengyin formation

The Mengyin Formation was originally considered to beEarly Cretaceous (?Neocomian) in age by Wiman (1929).Subsequently, a Late Jurassic age (early Tithonian) was sug-gested on the basis of the dinosaurian fauna (Young 1958;Mateer & McIntosh 1985; Dong 1992) and conchostrachans(Chen et al. 1982), which has been accepted by most authors(e.g. Weishampel 1990; Barrett et al. 2002; Weishampel etal. 2004). However, X.-C. Wu et al. (1994:227) consideredthe co-occurrence of the crocodyliform Shantungosaurus andthe turtle Sinemys as evidence that the Mengyin Formationwas correlated with Early Cretaceous deposits in the Luo-handong Formation of Inner Mongolia, which is consideredBarremian in age (ca. 130–125 Ma; Averianov & Skutschas2000). Dong (1995:94) likewise referred the Mengyin Groupto the Early Cretaceous Psittacosaurus Complex (ca. 120 Ma;H.-Y. He et al. 2004). More recently, Barrett & Wang (2007)described Euhelopus-like teeth from the Yixian Formationthat led them to infer a possible Aptian age for the MengyinFormation. There is a growing consensus that the MengyinFormation is Early Cretaceous, rather than Late Jurassic inage, although more specific determination is not yet possible.Accordingly, we ascribe an age range of Barremian–Aptian(ca. 130–112 Ma) to Euhelopus zdanskyi.


Table 1 Classification of the Chinese sauropods Euhelopus (= Helopus), Tienshanosaurus, Omeisaurus, Mamenchisaurus and Shunosaurus.

Reference Higher taxon Content

Wiman 1929 Helopodinae: Cardiodontidae(= Cetiosauridae)

Helopus

Young 1937 Morosauridae: Helopodinae HelopusTienshanosaurus

Young 1939 Brachiosauridae: Helopodinae HelopusOmeisaurusTienshanosaurus

Lapparent & Lavocat 1955 Titanosauridae HelopusRomer 1956 Brachiosauridae: Euhelopodinae Euhelopus

OmeisaurusTienshanosaurus

Young 1958 Bothrosauropodidae: Astrodontidae HelopusOmeisaurusTienshanosaurus

Homalosauropodidae: Titanosaurinae MamenchisaurusSteel 1970 Camarasauridae: Euhelopodinae Euhelopus

MamenchisaurusOmeisaurusTienshanosaurus

Young & Zhao 1972 Homalosauropodidae: Mamenchisauridae MamenchisaurusHomalosauropodidae Omeisaurus

TienshanosaurusBothrosauropodidae: Euhelopodidae Euhelopus

Dong et al. 1983 Camarasauridae: Cetiosaurinae ShunosaurusCamarasauridae: Euhelopodinae Mamenchisaurus

OmeisaurusX. He et al. 1988 Mamenchisauridae ‘Helopus’

MamenchisaurusOmeisaurus

Zhang 1988 Cetiosauridae ShunosaurusMcIntosh 1990 Camarasauridae: Camarasaurinae Euhelopus

TienshanosaurusDiplodocidae: Mamenchisaurinae MamenchisaurusCetiosauridae: Shunosaurinae Omeisaurus

ShunosaurusUpchurch 1995, 1998 Eusauropoda: Euhelopodidae Euhelopus

MamenchisaurusOmeisaurusShunosaurus

Dong 1998 Camarasauroidea: ‘Euhelopidae’ EuhelopusCamarasauroidea: Mamenchisauridae Mamenchisaurus

OmeisaurusCamarasauroidea: Barapasauridae Shunosaurus

Wilson & Sereno 1998 Somphospondyli EuhelopusEusauropoda Omeisaurus(paraphyletic series) Shunosaurus

Martin-Rolland 1999 Euhelopodidae: Euhelopodinae Euhelopus(= Tienshanosaurus)MamenchisaurusOmeisaurus

Euhelopodidae: Shunosaurinae ShunosaurusTang et al. 2001a Mamenchisauridae Mamenchisaurus

OmeisaurusOuyang & Ye 2002 Mamenchisauridae Mamenchisaurus

Omeisaurus


Table 1 Continued.

Reference Higher taxon Content

Wilson 2002 Somphospondyli EuhelopusEusauropoda: Omeisauridae Mamenchisaurus

OmeisaurusEusauropoda Shunosaurus

Upchurch et al. 2004a Eusauropoda Euhelopus(paraphyletic series) Mamenchisaurus

OmeisaurusShunosaurus

This analysis Somphospondyli EuhelopusEusauropoda (paraphyletic series) Mamenchisaurus

OmeisaurusShunosaurus

Systematic palaeontology

DINOSAURIA Owen, 1841SAURISCHIA Seeley, 1887SAUROPODA Marsh, 1878

NEOSAUROPODA Bonaparte, 1986TITANOSAURIFORMES Salgado et al., 1997

Euhelopus Romer, 1956

Euhelopus zdanskyi (Wiman 1929) Figs 5–25;Supplementary Data Figs 1–5 “Supplementary data”available on Cambridge Journals Online: http://www.journals.cup.org/abstract S1477201908002691

HOLOTYPE. PMU 233 (exemplar a) and exemplar c (the lat-ter’s accession number and whereabouts are unknown; X.Xing, pers. comm., 2007). Exemplar a comprises a par-tial skull (right and left premaxillae, maxillae, lacrimals,quadratojugals and palatines, left nasal, left postorbital, leftsquamosal, right quadrate, right pterygoid) and lower jaws(right and left dentaries, surangulars, angulars, left preartic-ular), 28 articulated presacral vertebrae, a left scapula, leftcoracoid, left humerus and left femur (Fig. 2; Wiman 1929;Mateer & McIntosh 1985; Young 1935).

LOCALITY AND HORIZON. Mengyin Formation, centralShandong Province, China (Fig. 1). The age of the MengyinFormation remains controversial, but correlation with otherunits in Asia suggests an Early Cretaceous age.

REFERRED SPECIMENS. PMU 234 (exemplar b), which in-cludes an articulated series of nine dorsal vertebrae and asacrum, two dorsal ribs, a nearly complete pelvis and righthindlimb lacking metatarsal V and several pedal phalanges(Fig. 2).

Britt (1993:125–128) tentatively referred to Euhelopusan isolated, nearly complete, posterior cervical vertebra(IVPP 10601) from the Shishougou Formation (JunggarBasin) of China. He identified small, thin-walled chambers(camellae) extending throughout the interior of the centrumand neural arch (Britt 1993: fig. 14) and on that basis ques-tioned McIntosh’s (1990) allocation of Euhelopus to Ca-marasauridae. IVPP 10601 differs from Euhelopus cervicalvertebrae in its nearly circular centrum cross-section, largepleurocoels, relatively short centrum and tall neural spine.However, we agree with Britt (1993) that camellate pneu-

maticity is evidence against phylogenetic affinities with Ca-marasaurus.

Ruiz-Omenaca et al. (1997) and Canudo et al. (2002)described isolated Euhelopus-like teeth from the lowerBarremian (Lower Cretaceous) of La Cantalera (Teruel),Spain and proposed an Early Cretaceous geographicalconnection between Europe and Asia. Canudo et al. (2002:figs 2–3) defended this claim on the basis of prominent“cingular cusps”, which is their term for the lingual crownbuttresses that are, thus far, only known in Euhelopuszdanskyi (Wilson 2002: appendix C). Buffetaut et al.(2002) described several isolated euhelopodid teeth fromthe Phu Kradong Formation of Dan Luang in northeasternThailand. They drew attention to their close resemblance toOmeisaurus and Mamenchisaurus, genera that are no longerconsidered to be closely related to Euhelopus (and thereforenot euhelopodids; see below). Nevertheless, nearly all of theDan Luang teeth possess the autapomorphic lingual crownbuttress that characterises Euhelopus. Likewise, Barrett &Wang (2007) referred isolated teeth from the Lower Creta-ceous Yixian Formation of China that also bear these distinctlingual crown buttresses. This shared unique feature suggeststhat the La Cantalera, Dan Luang and Yixian specimensare closely allied to Euhelopus, but more material is neededbefore referral to the genus and species can be justified.

REVISED DIAGNOSIS. Procumbent teeth with asymmetricalcrown-root margin (i.e. the mesial margin is closer to theapex of the crown) and well developed crown buttresseson mesiolingual crown surface, axis with postspinous fossacontaining three coels, cervical 3 neural spine with later-ally compressed, anteriorly projecting triangular process,postaxial cervical vertebrae with variably developed epi-pophyses and more subtle ‘pre-epipopophyses’ below theprezygapophyses, cervical neural arches with epipophyseal–prezygapophyseal lamina separating two pneumatocoels,cervical pleurocentral openings reduced to foramina, cervicalneural spines reduced anteroposteriorly and dorsoventrally,anterior cervical vertebrae with three costal spurs on tuber-culum and capitulum, middle cervical ribs hang well belowcentrum margin due to elongate parapophyses and capitula,presacral neural spines 11–30 divided, presacral neural spines16–21 “trifid” with median tubercle as large or larger thanmetapophyses, middle and posterior dorsal parapophysealand diapophyseal laminae cross to form “K” configuration,presacral pneumaticity extending into the ilium.


Figure 4 Cladistic hypotheses of the relationships of Chinese sauropods (in bold-face type) to other sauropod genera. For simplicity, someterminal taxa have been combined into suprageneric taxa.

Description

The anatomy of Euhelopus zdanskyi exemplars a and b wascarefully described by Wiman (1929), and Young (1935) de-scribed and illustrated key limb elements of exemplar c thatwere not preserved in exemplars a and b. The skull of Eu-

helopus exemplar a was redescribed by Mateer & McIntosh(1985), who reidentified several elements, provided moreanatomical detail and reconstructed the skull in lateral view.Although we comment on specific aspects of the skull, ourredescription focuses on the vertebral, pelvic and hindlimbelements, which were not discussed by Mateer & McIntosh


Figure 5 Photograph of Otto Zdansky examining Euhelopuszdanskyi exemplar b within its glass-enclosed mount in the 1950s.Photograph kindly provided by Museum of Evolution, UppsalaUniversity.

(1985). In the description that follows, we draw attentionto morphological features of the vertebral and appendicularskeleton that will help elucidate its phylogenetic relation-ships, many of which have not been discussed previously.Where appropriate, we note where our interpretation differsfrom Wiman (1929), which we have translated from the Ger-man. All quoted passages are from the translation by N. In-sel, which is available at the Polyglot Paleontologist website(http://www.paleoglot.org/index.cfm).

Exemplars a and b have been mounted within a displayenclosure at the Palaeontological Museum in Uppsala sincethe 1930s (Fig. 5). Only the skull, axis, cervical 3 and thepes can be removed; all other elements are fixed in theiroriginal positions. We have reproduced the excellent platesillustrating Wiman’s monograph (Supplementary Data Figs1–4) because they furnish the only views of certain elementsthat can no longer be accessed due to the constraints of thedisplay enclosure (e.g. top of sacrum) or the way the speci-men was mounted (e.g. articular surfaces of vertebrae). Wesupplement these figures with photographs and diagrams ofspecific areas of interest (Figs 6–26). Our description usestraditional orientational descriptors and anatomical termin-ology (i.e. Romerian terms), rather than standardised termsfrom the Nomina Anatomica Avium or Nomina AnatomicaVeterinaria, which apply to birds and domesticated mam-mals, respectively (see discussion in Wilson 2006).

Skull (Fig. 6; Supplementary data Figs 1, 2)

The skull of Euhelopus was described and figured in theoriginal monograph by Wiman (1929: pls 1–2) and then re-described by Mateer & McIntosh (1985: figs 1–5). Here,therefore, we do not attempt a comprehensive redescription,but focus instead on new observations and amendments.

PRESERVATION OF CRANIAL ELEMENTS. The preserved cra-nial elements include paired premaxillae, maxillae, lacrimals,

quadratojugals and palatines, a left nasal, left postorbital, leftsquamosal, right quadrate, right pterygoid, paired dentaries,surangulars, angulars and a left prearticular. The premaxil-lae, maxillae and dentaries contain several teeth in situ, butthe collection also includes at least 9 isolated teeth that pre-sumably belonged to exemplar a.

Wiman (1929:7) provided some information on the stateof preservation of the skull when first discovered: “the skullwas disarticulated but the appropriate elements were lyingon top of each other and side by side within a small lim-ited area in front of the axis. In several cases the bones layso close to each other that it was difficult to separate themespecially because some were very thin. Perhaps it is be-cause the skull disarticulated before being buried and crushedby the overlying sediment that the bones are so undeformedthat the skull when rebuilt is only slightly more asymmetricalthan it would have been in life.”

PREMAXILLA. Both premaxillae are preserved virtually in-tact except for the loss of the middle and upper portionsof the ascending process, which would normally form mostof the internarial bar. The premaxilla resembles that of othernon-diplodocoid sauropods, with a robust tooth-bearing mainbody, ascending process and posterolateral process. The re-gion where the ascending process meets the main body isslightly damaged on both sides, but it is clear that this pro-cess was offset a little posteriorly relative to the anteriormargin of the main body. This step-like offset is seen inmost non-diplodocoid sauropods (Wilson 2002; Upchurchet al. 2004a), although it is not developed as stronglyin Euhelopus as it is in Camarasaurus (Madsen et al.1995) or Brachiosaurus (Janensch 1935–36). The premax-illary posterolateral process is subtriangular in outline andforms a thin sheet of bone that has been incorporated intothe floor of the external narial fossa, which cannot beseen clearly in lateral view. The ventrolateral margin ofthe posterolateral process contacts the dorsal edge of theanterior ramus of the maxilla and extends posteriorly ontothe base of the maxillary ascending process. The dorsomedialmargin of the posterolateral process merges into the posteriorpart of the base of the internarial bar. As a result, the left andright posterolateral processes create a deep, narrow grooveextending vertically up the posterior midline of the base ofthe internarial bar. Thus, although the premaxillae and maxil-lae form an external narial fossa, the medial portions of thesebones do not contact each other on the midline. The basesof the premaxillary teeth are supported labially by a vent-ral extension of the lateral surface of the premaxillary mainbody (i.e. the “lateral plate”). This structure is also seen inthe maxillae and dentaries. The subnarial foramen is a small,elliptical opening that lies on the premaxilla–maxilla suture.It is visible in lateral view, but lies within the external narialfossa. The foramen faces mainly laterally and a little dorsally.

MAXILLA. The maxillary ascending process is directed pos-terodorsally in lateral view. There is a small preantorbitalfenestra that pierces the body of the maxilla below the pos-teroventral corner of the antorbital fenestra (Fig. 6). The fen-estra is matrix-filled and was not noticed previously (Mateer& McIntosh 1985; Upchurch 1995, 1998; Wilson & Sereno1998; Wilson 2002; Upchurch et al. 2004a). The antorbitalfenestra lies flush with the lateral surface of the snout; i.e.there is no antorbital fossa on the maxillary ascending process


Figure 6 Euhelopus zdanskyi exemplar a (PMU 233). Stereophotographs of right premaxilla and maxilla in medial view, showingpreantorbital fenestra (paof) and lingual crown buttresses (lcb). Scale bar = 5 cm.

or lacrimal. The presence of an articular area for the lacrimalon the posterior part of the dorsal margin of the maxilla sug-gests that the jugal made very little, if any, contribution tothe margin of the antorbital fenestra.

NASAL. We interpret the bone identified as the right frontalby Mateer & McIntosh (1985: fig. 1c–d) to be the left nasal.This element was not described or figured by Wiman (1929).It is very thin dorsoventrally (maximum thickness equals ap-proximately 3 mm) and bowed slightly upwards so that ithas a mildly concave ventral surface and correspondinglyconvex dorsal surface. Sauropod nasals are generally thin-ner than the frontals, and Mateer & McIntosh (1985:125)stated that: “It is a thinner bone than [the frontal] in Ca-marasaurus.” There are two projections that we interpret asanteromedial and anterolateral processes. The anteromedialprocess would have met its partner on the midline to form theposterior part of the internarial bar, and the anterolateral pro-cess would have contacted the maxillary ascending process,prefrontal and lacrimal at the corner of the antorbital fenes-tra. The anteromedial process is relatively long but brokenat its anterior end. The anterolateral process is shorter, moreslender and subtriangular in dorsal outline. The area betweenthese processes is broadly concave and in our interpretationrepresents the posterior margin of the external naris. On theventral surface, a low, rounded ridge extends along the anter-olateral process and then divides into two branches at its base.One branch extends along the lateral margin of the bone tothe posterior edge, whereas the other follows the undersideof the possible narial margin and fades out midway betweenthe bases of the two processes. Mateer & McIntosh’s (1985)identification of this element as a frontal was supported by thepresence of a subdued ridge on the ventral surface for articu-lation with the laterosphenoid and orbitosphenoid. However,the orientations of the ridges on the ventral surface do notconform to those expected in a frontal, and they also lack theirregular transverse ridges and grooves characteristic of thesuture between frontal and braincase elements, as well as theorbital ornamentation present on most saurischian frontals.

POSTORBITAL. The postorbital is triradiate with a long,anteroventrally-directed jugal process. The orientation ofthe anteromedial and posterior processes suggest that theupper temporal bar was displaced ventrally in Euhelopus,so that the supratemporal fenestra would have been visiblein lateral view, as in most eusauropods (Wilson & Sereno1998). The posterior process articulates with a corresponding

triangular notch in the lateral surface of the squamosal, andit is clear that the latter element formed the posterior marginof the supratemporal fenestra. Consequently, Euhelopuslacked the derived exclusion of the squamosal from the mar-gin of the supratemporal fenestra by a postorbital–parietalcontact, which is a synapomorphy of Nemegtosaurus andQuaesitosaurus (Upchurch 1995, 1998, 1999; Wilson 2002,2005a). The morphologies of the postorbital and squamosaltogether suggest that the supratemporal fenestra opened dor-solaterally, was wider transversely than anteroposteriorly,and was relatively large compared to the width across theskull roof. The jugal process of the postorbital has a sub-triangular transverse cross-section that is wider transverselythan dorsoventrally. This derived state is characteristic ofEusauropoda (Wilson & Sereno 1998). The absence of thejugal and the incomplete preservation of the jugal process ofthe postorbital make it difficult to reconstruct the shape ofthe lateral temporal fenestra. However, the postorbital indic-ates that this fenestra extended forwards below the orbit andEuhelopus was probably as derived in this respect as otherneosauropods.

SQUAMOSAL. The left squamosal is mounted upside-downin the skull in the position of the right squamosal (Mateer &McIntosh 1985; see Supplementary Data Fig. 1). The pre-served portion includes the ventral process, the articulationfor the postorbital and the lateral part of the main body (i.e. asubstantial part of the main body is missing medially, contraMateer & McIntosh 1985). The ventral process is formedfrom very thin bone that is directed anteroventrally in itsproximal part, but distally it extends ventrally. This processtapers to a sharp point in lateral view, although this mayhave been exaggerated by breakage. The thin sheet of boneis curved in horizontal cross-section, with a mildly convexanterolateral face and corresponding concave posteromedialface. The latter represents the area that covered the anterolat-eral part of the quadrate shaft in life. The anterolateral surfaceof the ventral process forms part of a fossa surrounding thelateral temporal fenestra. As the ventral process joins themain body, its anterior part is embayed medially with respectto the posterior part. The latter region is the lateral surfaceof the main body and this forms a ridge that curves upwardsand forwards to define the dorsal margin of the lateral tem-poral fenestra and the lower boundary of the triangular slotfor the posterior process of the postorbital. The region forreception of the postorbital is particularly large and deep and


subtriangular but is thin-walled medially. The medial sur-face of the postorbital articulation is mildly concave and iscontinuous with the anterior face of the main body of thesquamosal. Ventrally, this medial surface is delimited by aridge, which projects medially as it extends anteroventrally;this forms the roof of the fossa for the quadrate.

QUADRATOJUGAL. Both the left and right quadratojugals arealmost completely preserved, lacking only the end of theirdorsal processes. The anterior process of the quadratojugal isvery long and slender at its base, where it has a subtriangularcross-section. Its dorsolateral surface is slightly excavated,marking the ventral margin of the lateral temporal opening.Towards its anterior end, this process widens vertically toform a laterally-compressed, rounded plate. The dorsal pro-cess projects perpendicular to the anterior one, and the twomerge smoothly into each other at the posteroventral cornerof the bone. The dorsal process expands both anteroposteri-orly and mediolaterally above its junction with the anteriorprocess and then tapers to a point at its anterodorsal tip. Itsdistal extreme is broken away, and its length relative to thelength of the anterior process cannot be stated with certainty.The anterior part of the lateral surface of the dorsal processis slightly excavated. This excavation narrows towards itsventral end and may represent evidence for a contact withthe ventral process of the squamosal. Such a quadratojugal–squamosal contact is the plesiomorphic state found in mostsauropods except diplodocoids (Upchurch 1998; Upchurchet al. 2004a).

QUADRATE. The right pterygoid and quadrate were found inarticulation (Wiman 1929:8), although a break just posteriorto the ectopterygoid process may mean that the two elementsare no longer in their correct relative orientation (Mateer &McIntosh 1985). The shape of the quadrate, its articulationwith the pterygoid and the 90◦ angle between the anterior anddorsal rami of the quadratojugal, all suggest that the quad-rate in Euhelopus was orientated nearly vertically, as in mostsauropods, and therefore did not display the derived anter-oventrally slanting orientation found in diplodocoids. Wiman(1929:8) stated: “from the back a big foramen quadrati is vis-ible between the quadrate and the quadratojugal.” As Mateer& McIntosh (1985) noted, this implies that the quadrato-jugal formed the lateral wall of the fossa, whereas in factthis is formed by the quadrate. Although the true depth ofthe fossa is obscured by matrix, Euhelopus clearly possessesthe derived “deep” fossa also found in macronarians, somediplodocoids such as Limaysaurus (= “Rebbachisaurus” and“Rayososaurus”) tessonei (Calvo & Salgado 1995; Upchurch1998) and some non-neosauropod eusauropods (e.g. Ma-menchisaurus sinocanadorum, Russell & Zheng 1993). To-wards the dorsal end of this fossa, the lateral margin curvesmedially to partially enclose this region. However, the ex-tent of this closure cannot be determined because of break-age. The distal (articular) end of the quadrate is damaged,but its surface slopes ventromedially to an anteroposteriorly-expanded region, as in other sauropods (Upchurch & Barrett2000).

PTERYGOID. The pterygoid of Euhelopus was described ashaving a unique shape among sauropods (Mateer & McIn-tosh 1985). In particular, the anterior process is a flat plateof bone, with a rounded spatulate lateral profile, that projectsupwards into the anterior part of the orbit. The anterior and

ectopterygoid processes are also deflected laterally at an un-natural angle that would make articulation with the palatineand vomer very difficult if these latter bones had been pre-served in situ. This deflection also makes the ectopterygoidprocess appear much smaller in lateral view than it wouldhave been in life.

Anterior to the fractured area, the pterygoid is heavilyreconstructed and it is, therefore, difficult to determine itsoriginal morphology. However, there is a faint ridge on thelateral surface of the anterior process, close to its ventral mar-gin, that extends forwards from the base of the ectopterygoidprocess to approximately half way along the anterior process.This ridge may have articulated with the palatine.

There is little information on the position and morpho-logy of the fossa for articulation with the basipterygoid pro-cess. The region on the medial surface, just above the base ofthe ectopterygoid process, is damaged and the approximateposition of the articular fossa is now occupied by a smallbroken mass of bone. The finger-like process that curvesaround the tip of the basipterygoid process in the pteryg-oids of Brachiosaurus and Camarasaurus (Upchurch 1998;Wilson & Sereno 1998) appears to be absent in Euhelopus,but this may have been caused by poor preservation. Thequadrate articulation resembles those found in other sauro-pods.

PALATINE. The elements that Wiman (1929; SupplementaryData Fig. 2) identified as vomers were reidentified by Mat-eer & McIntosh (1985: fig. 2c–d) as palatines. Although thepalatine of Euhelopus differs in some respects from thoseof Camarasaurus (Madsen et al. 1995: figs 5, 38) and par-ticularly Brachiosaurus (Janensch 1935–36: figs 33–35), asnoted by Mateer & McIntosh (1985), we nevertheless agreewith their identification.

The palatine is roughly triangular in medial and lateralviews, with a rounded ventral portion and a platelike dorsalportion. The right and left palatines are nearly completelypreserved, and lack only a portion of their dorsal blade. Theleft palatine appears to be slightly more distorted than theright. Anteriorly, the rounded ventral portion of the palat-ine extends forward as a rodlike process that terminates ina flattened, subcircular articulation for the maxilla, as in alleusauropods (Wilson 2002). In medial view, the ventral por-tion of the palatine is rounded and contacted the pterygoid.In lateral view, the ventral portion of the palatine forms asharpened edge that contacted the ectopterygoid. The ecto-pterygoid articulation probably continued dorsally onto theblade of the palatine, but its exact extent is difficult to de-termine in the absence of an ectopterygoid. The dorsal bladeof the palatine is thin and reaches its peak anteriorly, nearthe neck of the maxillary process. The blade of the pal-atine is straight in Euhelopus and Camarasaurus (Madsenet al. 1995), unlike the curved blade present in Brachiosaurus(Janensch 1935–36). In lateral view, a thick vertical ridgeoccupies the anterior portion of the blade; behind it is asubtriangular fossa some portion of which contacted the ect-opterygoid. The inverse of this topography can be seen on themedial side of the dorsal blade, which bears a vertical fossaanteriorly and a more prominent posterior portion. Based oncomparisons with Camarasaurus (Madsen et al. 1995), thevomer probably articulated in the fossa on the anteromedialedge of the dorsal blade of the palatine.


DENTARY. Complete right and left dentaries are preserved.The dentary increases slightly in depth towards the sym-physis, as in most sauropods (Wilson & Sereno 1998;Upchurch & Barrett 2000). The long axis of the symphysealarticular surface is orientated at approximately 110◦ relativeto the long axis of the jaw. The ventral margin of the mand-ible, at its anterior end, is gently rounded and lacks the sharp,triangular, chin-like projection found in some diplodoc-oids (Upchurch 1998; Wilson 2002). The parasagittally-orientated posterior part and transverse anterior part of thedentary merge smoothly into each other to form a mandiblethat is U-shaped in dorsal view. Thus, Euhelopus resemblesBrachiosaurus and Camarasaurus in this regard and does notdisplay the more rectangular dorsal mandibular profile seenin diplodocoids.

SURANGULAR. The dorsal margin of the right surangular hasbeen damaged and it is therefore not possible to assess theheight of this bone relative to that of the angular.

ANGULAR. Most of the left angular is preserved, althoughthe anterior and posterior ends appear slightly damaged andthe exact length and outline of the bone cannot be determinedprecisely. The angular is a long, plate-like bone that is ori-entated vertically and bears a transversely thickened ventralrim. The ventral margin is slightly concave in lateral viewand the dorsal margin is more strongly convex. The ventralthickening is created by a medial expansion that underlies anexcavated area on the anterior part of the medial surface. Thisventral medial shelf is most prominent anteriorly. There isno indication that the angular, surangular, or dentary formedany part of the margin of an external mandibular fenestra andit seems very likely that the latter was closed in Euhelopusas in most eusauropods (Upchurch 1998; Wilson & Sereno1998). There are no foramina penetrating from one side ofthe angular to the other. In dorsal view the angular is slightlybowed laterally although this is exaggerated by the presenceof the medially-directed ventral shelf.

DENTITION. Wiman’s (1929) description of the teeth of Eu-helopus is brief and focuses on macrowear and the relativepositioning of the crowns. Mateer & McIntosh (1985) did notdescribe the teeth at all. A detailed description of the teethis, therefore, provided below.

There are four teeth in each premaxilla, 10 in each max-illa and 13 in each dentary. Previously published figures andphotographs of the tooth-bearing elements show the teethprojecting somewhat anteriorly, roughly parallel to the sym-physis. The enamel margin at the crown–root junction isasymmetrical – slanting apically towards the mesial side –indicating that the procumbent orientation of the teeth isa genuine feature rather than the result of distortion. Thelargest teeth are situated at the anterior ends of the upperand lower jaws. As in most sauropods, apart from narrow-crowned forms such as Diplodocus and titanosaurs, adjacentteeth in Euhelopus contact each other and are arranged in aslightly overlapping “imbricate” pattern (Wilson & Sereno1998; Wilson 2002). The tooth crowns expand very slightlymesiodistally immediately adjacent to the root, but not prom-inently to form the broad spatulate crowns found in Camara-saurus and several basal eusauropods such as Omeisaurus.The Euhelopus teeth then taper towards relatively narrowapices. As a result, the Euhelopus crowns are more parallel-sided in labial view, like those of Brachiosaurus and several

other basal titanosauriforms. The slenderness indices (SI),maximum crown length divided by maximum mesiodistalwidth (Upchurch 1998), for in situ teeth from the left premax-illa, maxilla and dentary, are close to 2.0 or less. The labialsurface of each crown is convex both mesiodistally and to-wards the apex, with a narrow groove (or change of angle)extending from root to apex near both the mesial and distalmargins of the crown. The lingual surface is mildly concave.This concavity is created by the slight lingual deflection ofthe crown apex and the lingual curvature of the mesial anddistal margins. However, within the lingual concavity is aprominent ridge that extends from the root to the apex, vir-tually filling the lingual concavity: consequently, the crownsare D-shaped in horizontal cross-section (Wilson & Sereno1998).

One of the most distinctive features of these teeth is arounded boss-like structure on the lingual part of each me-sial and distal margin, close to the base of the crown (Wilson2002; Fig. 6). These lingual crown buttresses have also beenobserved in unnamed Early Cretaceous sauropod teeth fromSpain (Canudo et al. 2002), Thailand (Buffetaut et al. 2002)and China (Barrett & Wang 2007), as mentioned above. Asin virtually all other sauropod teeth and several basal saur-opodomorphs (Upchurch et al. 2007), the tooth enamel inEuhelopus has a characteristic wrinkled or reticulate texture(Wilson & Sereno 1998; Wilson 2002). The macrowear tendsto be in the form of concave facets on the mesial and distalmargins close to the apex, creating “shoulders” on worn teeth,as also occurs in Camarasaurus and many basal eusauropods(Upchurch & Barrett 2000). The flat, high-angled apical wearfacets observed in Brachiosaurus and many titanosaurs areabsent in Euhelopus (Upchurch & Barrett 2000). Apart fromchanges in size, there are no observable differences in crownmorphology along the jaws from mesial to distal, or betweenthe upper and lower jaws. No denticles have been found onthe teeth of Euhelopus. Recent examination of microwear onisolated Euhelopus crowns collected with exemplar a showsscratches that are roughly parallel to the tooth axis (P. Barrett,pers. comm., 2007).

Vertebral column (Figs 7–23; Supplementary DataFigs 3, 4)

Euhelopus exemplars a–c preserve overlapping sections ofvertebrae that together form a series from the axis to the lastsacral vertebra. Wiman (1929) did not estimate the positionof the cervicodorsal or dorsosacral boundaries, but he didestimate that the first vertebra of exemplar b corresponds tothe 22nd vertebra from the skull in exemplar a, which im-plies 36 precaudal vertebrae. We agree with this estimateand below discuss our justifications for positioning the cer-vicodorsal and dorsosacral boundaries. Although we wereable to establish that there are six sacral vertebrae and 30presacral vertebrae, the position of the cervicodorsal bound-ary is ambiguous, because the 18th vertebra from the skullbears features of both the cervical and dorsal region of theaxial column. We provisionally suggest that Euhelopus had17 cervical, 13 dorsal and 6 sacral vertebrae.

Although exemplar a and exemplar b are nearly thesame size, they exhibit slightly different states of fusion ofvertebral sutures. Exemplar a bears no trace of neurocentralsutures nor sutures between the postaxial cervical verteb-rae and their associated ribs. Exemplar b, in contrast, bears


Figure 7 Euhelopus zdanskyi exemplar a (PMU 233). Axis vertebra in left lateral (A) and right posterolateral (B) views. Abbreviations used forvertebrae figs: acdl, anterior centrodiapophyseal lamina; acpl, anterior centroparapophyseal lamina; ca, capitulum; cpol,centropostzygapophyseal lamina; co, coel; cprl, centroprezygapophyseal lamina; csp, costal spurs; di, diapophysis; epi, epipophysis; eprl,epipophyseal–prezygapophyseal lamina; fl, flange; fo, fossa; nsp, neural spine; p, parapophysis; pc, pleurocoel; pcdl, posteriorcentrodiapophyseal lamina; pcpl, posterior centroparapophyseal lamina; ppdl; parapodiapophyseal lamina; podl, postzygodiapophyseallamina; poz, postzygapophysis; prdl, prezygodiapophyseal lamina; prpl, prezygoparapophyseal lamina; prepi, pre-epipophysis; prz,prezygapophysis; spol, spinopostzygapophyseal lamina; sprl, spinoprezygapophyseal lamina; tlp, triangular lateral process; tu, tuberculum;Arabic numbers refer to pneumatic coels described in text. Scale bar = 5 cm.

partially fused neurocentral sutures that can be identified onthe lateral aspect of all dorsal vertebrae. However, exemplarsa and b overlap only across six vertebrae, and the differencein maturity between the two specimens may be attributed tothe fact that exemplar b consists of the posterior portion ofthe presacral column, and exemplar a consists of the anteriorportion. The neurocentral sutures of posterior dorsal verteb-rae typically fuse later than those of cervical and anteriordorsal vertebrae in Camarasaurus (Ikejiri et al. 2005).

The cervical, dorsal and sacral vertebrae all show signsof pneumaticity. As will be discussed below, slight regionaldifferences in the extent and nature of pneumaticity arepresent. We employ the nomenclature for vertebral laminaeand associated abbreviations proposed by Wilson (1999),with appropriate additions to this system to accommodatethe unusual structures found in Euhelopus. The abbreviationsfor laminae are used in the text after the first usage of eachterm; abbreviations appear in uppercase, and their plurals arefollowed by a lowercase “s” (e.g. spinopostzygapophyseallaminae = “SPOLs”).

We note here that the Roman numerals written directlyon the vertebrae (and visible in photographs) differ by onefrom those numbers discussed and labelled in Wiman (1929),which are their inferred position in the series. The inkednumbers on the vertebrae correspond to their position in thepreserved series, which does not include the atlas. The axisvertebra is numbered “I” because it was the first preservedcervical (Fig. 7), but is labelled with a Roman numeral “II”in the figures of Wiman (1929). In the interest of brevity,the description below refers to vertebrae by their region and

number (e.g. “cervical 1”, “dorsal 4”) rather than by morecomplete descriptors (i.e. “first cervical vertebra”, “fourthdorsal vertebra”).

Cervical vertebrae (Figs 7–13; Supplementary DataFig. 3)

Exemplar a includes a complete, articulated cervical seriesextending from the axis to cervical 17. All cervical vertebraeshow the camellate pneumatic structure that is character-istic of titanosauriform sauropods (Upchurch 1998; Wilson& Sereno 1998; Wedel et al. 2000). Pneumaticity extendsthroughout the entirety of the centrum and neural arch inall cervical vertebrae. The extent of pneumatisation can beconfirmed in fortuitous breaks in the external bone surfacewhere pneumatic chambers are exposed, but it can also beinferred without these breaks, where the external bony sur-face conforms to the internal pneumatic chambers (e.g. seeFigs 9–12, 14, below).

AXIS (Fig. 7; Supplementary Data Fig. 3). The axis is wellpreserved, but has been damaged posterolaterally on its rightside. A portion is missing from the centrum, the right postzy-gapophysis is absent and the neural spine is distorted and thebase of its anterior margin has been reconstructed.

The centrum is strongly pinched at midlength and bearsexpanded anterior and posterior ends. Ventrally, the centrumis gently concave anteroposteriorly and slightly convex trans-versely. The anterior articular surface is roughened and di-vided into low, rounded middle and upper portions that are


separated from the ventral and ventrolateral region by a deepgroove. This upper portion corresponds to the odontoid pro-cess (atlantal pleurocentrum). The parapophysis is marked bya low, roughened area at the extreme anteroventral corner ofthe lateral surface of the centrum. The long, shallow fossa onthe lateral surface of the centrum is a rudimentary pleurocoelthat is divided by a small, oblique lamina.

The diapophysis is best preserved on the left side andforms a process positioned just dorsal to the neurocentraljunction. Its base lies near the anterior end of the neuralarch, very close to the prezygapophysis, but the process it-self projects laterally, posteriorly and slightly ventrally. Low,rounded ridges extend from the base of the diapophysis andcorrespond to the four main diapophyseal laminae – anteriorand posterior centrodiapophyseal laminae (ACDL, PCDL),which extend along the top of the centrum and form thedorsal margin of the pleurocoel, a prezygodiapophyseal lam-ina (PRDL) and a prominent, curving postzygodiapophyseallamina (PODL).

The prezygapophysis is a small, triangular platform thatprojects laterally and slopes a little ventrally from the baseof the neural spine. It appears that the prezygapophyses wereseparated from each other on the midline by the tall, thinand anteriorly convex neural spine. The postzygapophysis isvery large and positioned high above the centrum. It projectsa short distance beyond the posterior margin of the centrum.This is the plesiomorphic state for sauropodomorphs anddiffers from the derived condition found in certain prosaur-opods, in which these processes terminate at the posteriormargin of the centrum (Sereno 1999; Yates & Kitching 2003;Upchurch et al. 2007). The postzygapophyseal articular sur-face is large, flat and elliptical. It faces downwards and curlsslightly ventrally towards its medial margin.

Plate-like SPOLs meet at the summit of the neural spineto form a deep postspinal fossa that is floored by thin intra-postzygoposphyseal laminae (TPOLs) that extend mediallyfrom the medial edge of each postzygapophysis. The medialsurface of the SPOL has three excavated areas that are sep-arated from each other by low ridges (Supplementary DataFig. 4B). These excavations become larger towards the an-terior region of this surface and appear to be an autapomorphyof Euhelopus (Wilson 2002). The summit of the neural spineis robust, thickened and positioned near mid-centrum. Anteri-orly, it slopes ventrally and forms a transversely compressedplate.

POSTAXIAL CERVICAL VERTEBRAE (Figs 8–13; Supplement-ary Data Fig. 3). The 15 postaxial cervical vertebrae (seediscussion of the cervicodorsal junction below) form a nat-ural series that was found in articulation (Wiman 1929). Thecervical vertebrae are in excellent condition, but there isminor damage to several parts of the series. The left postzy-gapophysis of cervical 3 is missing, cervical 4 and the spinesof cervicals 5 and 6 are poorly preserved, and the epipophysesof cervical 11 are broken.

All postaxial cervical centra are strongly opis-thocoelous, with a well-developed sub-hemispherical an-terior articulation and corresponding concave posterior ar-ticulation. As noted by Upchurch (1998), these articularsurfaces are taller than wide, an unusual condition that alsooccurs in Omeisaurus tianfuensis (X. He et al. 1988), Ma-menchisaurus hochuanensis (Young & Zhao 1972), Erketuellisoni (Ksepka & Norell 2006) and Shunosaurus lii (Zhang

Figure 8 Euhelopus zdanskyi exemplar a (PMU 233). Cervicalvertebra 3 in right lateral view. See Fig. 7 for abbreviations. Scalebar = 5 cm.

1988). The anterior articular ball is asymmetrical in lateralview, with its apex positioned dorsally. This condition is mostnoticeable in the anterior and middle cervical vertebrae (Figs8–11). The ventral edge of the posterior articular cup projectsmore posteriorly than the dorsal edge, as in other sauropods.The cervical centra are relatively long and slender throughoutmost of the series, but they become shorter anteroposteriorlyand increase in diameter towards the cervicodorsal junction(Table 2). In cervicals 3 and 4, the ventral surface of thecentrum is shallowly concave between the parapophyses butbecomes flat posteriorly. The ventral surfaces of cervicals5–17 are concave both longitudinally, because of the expan-ded articular ends, and transversely, due to sharp ridges thatextend along the ventrolateral edges of the centrum. Posteri-orly, these ridges become more flangelike and hang below thelevel of the centrum. There is a faint midline ridge within theanteriorly placed ventral depression in cervical 3, but this isabsent in all other cervical centra until it reappears in cervical17.

The postaxial cervical parapophyses lie at the anter-oventral margin of the centrum and are directed ventrolater-ally. The posterior margin of each parapophysis merges intothe ventrolateral ridge described above. The lateral surfaceof the centrum of cervical 3 has a small but sharp excava-tion that is divided by a ridge. The size and depth of thispleurocoel, and the prominence of the anterodorsally slopingoblique lamina that subdivides it, increase in more posteriorcervical vertebrae. By cervical 17 the pleurocoel is a deeppit, but the oblique lamina is absent.

The postaxial cervical neural arches are relatively lowand occupy the length of the centrum apart from the sectionimmediately below the postzygapophyses. As in other saur-opods, the height of the neural arch increases towards thecervicodorsal junction (Table 2).

The prezygapophyses are large processes that projectanteriorly and slightly laterally beyond the margin of the ar-ticular ball in dorsal view. They have flat articular surfacesthat face dorsomedially at an angle of about 30◦ above thehorizontal. They slope so that they face a little forwards.The size of the articular facets and the distance separatingthem increase in the posterior part of the series, especially


Figure 9 Euhelopus zdanskyi exemplar a (PMU 233). Cervical vertebra 8 in right lateral view. See Fig. 7 for abbreviations. Scale bar = 10 cm.

Figure 10 Euhelopus zdanskyi exemplar a (PMU 233). Cervical vertebra 10 in right lateral view. See Fig. 7 for abbreviations. Scale bar = 10 cm.


Figure 11 Euhelopus zdanskyi exemplar a (PMU 233). Cervical vertebra 14 and 15 in right lateral view. See Fig. 7 for abbreviations. Scalebar = 10 cm.

cervicals 16 and 17, as in other sauropods. Prezygapophysesare supported from below by a single, stout centroprezy-gapophyseal lamina (CPRL). Unlike diplodocids (Upchurch1998), the CPRLs of Euhelopus do not bifurcate dorsallyto form lateral and medial branches. These laminae are un-usual in Euhelopus because each gives rise to a short, bluntprocess just below the prezygapophysis. These structures re-semble the prominent epipophyses located above the postzy-gapophyses (see below) and are referred to here as “pre-epipopophyses”. These structures are also present in othersauropods, such as Erketu (Ksepka & Norell 2006). In theanterior cervical vertebrae, the prezygapophyses extend pos-teromedially and meet each other on the midline at the top ofthe neural canal opening via intraprezygapophyseal laminae(TPRLs). Despite the increasing height of the middle andposterior cervical neural arches, the TPRLs maintain theirclose association with the top of the neural canal, and thereis no “anterior midline lamina” (with coels on either side).Euhelopus differs in this respect from other sauropods suchas Apatosaurus (Gilmore 1936; Upchurch et al. 2004b) andCetiosaurus (Upchurch & Martin 2002).

In cervical 3, the diapophysis is situated at the neuro-central junction and projects ventrolaterally. It is suppor-ted posteriorly by the PCDL, which extends as a low ridgealong the neurocentral junction above the pleurocoel, fadingout well before the posterior margin of the arch. In sub-sequent cervical vertebrae, the diapophyses are positionedabove the neurocentral junction but below the level of thezygapophyses. They are supported by well-developed diapo-physeal laminae (PCDL, PRDL, PODL), as in other non-titanosaurian sauropods. The ACDL is generally poorly de-veloped or absent in the cervical vertebrae, but it can be seenas a short, anteroventrally-directed lamina in cervical 17 andthe dorsal vertebrae (see below). The PCDL is prominent andis directed posteriorly and a little ventrally in postaxial cer-vical vertebrae until cervical 17, where it becomes noticeablysteeper. There is a small pit in the infrapostzygapophyseal

fossa, just below the PODL and immediately above and be-hind the base of the diapophysis in cervicals 3 and 4, butthis coel is absent from cervical 5 onwards. The diapophysesthemselves remain relatively short processes that are directedlaterally and curve ventrally (i.e. they are “pendant”) as farposteriorly as cervical 17.

The postzygapophyses are well-developed processeswith gently concave articular surfaces that overhang the pos-terior end of the centrum. Each postzygapophysis is sup-ported from below by a stout CPOL. Despite the increasingheight of the neural arch in middle and posterior cervicalvertebrae, there is no evidence that Euhelopus possessedthe “posterior midline lamina” or associated coels presentin other sauropods (e.g. Cetiosaurus; Upchurch & Martin2002).

All postaxial cervical vertebrae bear a prominent epi-pophysis on the dorsal surface of each postzygapophysis.These structures continue into the dorsal series (see below).In the anterior and posterior cervical vertebrae (cervicals2–5, 11–17), the epipophyses are short and rounded, butin the middle cervical vertebrae (cervicals 6–10), they ex-tend posteriorly beyond the edge of each postzygapophysis(Figs 10–12). Each epipophysis is separated ventrally fromits respective postzygapophysis by a shallow groove. Thelateral margin of each epipophysis merges with the free lat-eral edge of each postzygapophysis, which together extendas a combined ridge across the neural spine to the base ofthe prezygapophysis. We term this ridge the epipophyseal–prezygapophyseal lamina (EPRL) and consider its presencethroughout the cervical series an autapomorphy of Euhelopusthat is also present in Nigersaurus (Sereno et al. 2007), Za-palasaurus (Salgado et al. 2006), Camarasaurus (Ostrom &McIntosh 1966: pls 10, 11) and in some theropods (e.g. Ra-jasaurus, Wilson et al. 2003; Stokesosaurus, Benson 2008).The neural arch laminae on the lateral aspect of the neuralspine (i.e. SPRL, SPOL) define a hollow that is divided intoan upper and lower coel by the EPRL (Figs 8–13). We term


Table 2 Measurements (in cm) of precaudal vertebrae of Euhelopus zdanskyi, taken from Wiman (1929:21).

Vertebral centrum The whole vertebraItemno.

Length withoutanterior convexity Posterior width Posterior height

Height of neuralspine

Width across outer edgesof postzygapophyses

Width acrossdiapophyses

a b a b a b a b a b a b

cv2 9.4 — 3.3 — 3.7 — 13.2 — 6.7 — 5.2 —cv3 13.0 — 3.6 — 4.8 — 10.8 — 7.3 — 8.3 —cv4 22.2 — 4.0 — 4.1 — 15.0 — 8.0 — 8.5 —cv5 23.4 — 4.6 — 6.5 — 15.8 — 8.8 — 9.1 —cv6 23.8 — 5.5 — 7.5 — 16.4 — 9.0 — 10.0 —cv7 26.0 — 6.6 — 8.2 — 20.2 — 9.4 — 11.6 —cv8 26.2 — 7.2 — 9.3 — 22.1 — 10.0 — 12.2 —cv9 27.4 — 7.4 — 9.6 — 23.3 — 10.7 — 13.7 —cv10 28.2 — 8.9 — 11.0 — 26.0 — 11.5 — 15.3 —cv11 28.3 — 9.3 — 11.5 — 27.4 — 12.6 — 15.8 —cv12 27.6 — 10.0 — 13.9 — 29.2 — 12.8 — 16.3 —cv13 26.8 — 11.3 — 12.7 — 31.0 — 13.4 — 19.4 —cv14 26.3 — 11.3 — 13.9 — 33.2 — 14.0 — 21.0 —cv15 26.3 — 12.3 — 14.2 — 33.7 — 16.5 — 23.0 —cv16 20.3 — 12.7 — 12.9 — 29.7 — 16.6 — 25.5 —cv17 18.0 — 14.8 — 14.2 — 27.3 — 17.0 — 31.1 —d1 14.2 — 13.1 — 14.2 — 27.9 — 17.5 — 32.3 —d2 12.8 — 12.0 — 13.2 — 31.1 — 16.3 — 37.2 —d3 10.1 — 11.0 — 13.2 — 32.1 — 15.8 — 38 —d4 11.6 — 9.8 — 13.3 — 35.1 — 12.0 — 37.4 —d5 12.2 10.3 9.2 13.3 13.3 14.5 39.3 29.8 12.1 16.2 32.6 46.6d6 12.8 12.0 9.2 12.0 13.8 12.0 44.0 31.6 11.3 12.7 29.5 41.5d7 12.7 11.0 — 11.8 — 11.0 44.2 32.3 10.0 13.0 24.2 37.9d8 — 11.2 — 11.2 — 11.9 — 35.8 9.4 12.4 21.6 34.0d9 — 10.3 — 13.2 — 12.3 — 36.7 — 11.3 — 30.7d10 — 8.0 — 11.3 — 14.1 — 37.1 — 11.0 — 26.6d11 — 9.3 — 11.6 — 13.8 — 38.0 — — — 25.4d12 — 10.3 — 13.8 — 14.4 — — — 10.2 — —d13 — 9.6 — 19.9 — 15.1 — — — 9.8 — 25.4s1 — 11.1 — 13.8 — 11.8 — 40.5 — 10.1 — 24.6s2 — 10.0 — 14.0 — — — 43.4 — — — 31.5s3 — — — — — — — 42.1 — — — 29.8s4 — — — — — — — 40.9 — — — 29.5s5 — — — — — — — 39.2 — — — 29.5s6 — — — — — — — 38.4 — — — —

Lower case “a” and “b” refer to exemplars a (PMU 233) and b (PMU 234); “cv”, “d” and “s” refer to cervical, dorsal and sacral vertebrae, respectively.

these coels, which are divided by a horizontal septum, “1h”and “2h” to distinguish them from similarly placed coelsin the dorsal series that are divided vertically (see below).The relative sizes and depths of “1h” and “2h” coels varyalong the cervical series in accordance with changes to theheight and length of the spine. In general, the lower coeltends to be smaller but deeper than the upper one. Begin-ning with the posterior cervical vertebrae (cervical 12), theEPRL terminates before reaching the prezygapophysis. As aresult, the coels are only divided posteriorly and merge intoeach other anteriorly. However, this appears to be a highlyvariable feature – for example, a more complete divisionbetween the upper and lower coels is still present on theleft side of cervical 13. The epipophyses continue into thedorsal series (see below), where they are represented by lowrounded projections that appear to be homologous to the tri-angular “aliform” processes present in Haplocanthosaurusand many macronarians (Upchurch 1998; Upchurch et al.2004a).

The greatest morphological variation along the cervicalseries occurs in the structure of the neural spine. The neuralspine remains relatively short throughout the cervical series,reaching its greatest height in middle cervical vertebrae andthen decreasing slightly towards the cervicodorsal junction(see Table 2). In the most anterior cervical vertebrae, theneural spine is built from robust plate-like SPRLs and SPOLsthat converge at a stout summit. Here, the SPRLs extend pos-teriorly, medially and dorsally, eventually merging into thebase of a single plate-like anterior spine margin. The up-per part of this anterior plate is developed into a laterallycompressed triangular process that projects forwards andoverhangs the prezygapophyses in cervical 3 (Fig. 8). Theequivalent area in cervical 4 is damaged and the anteriorlyprojecting triangular process is absent from cervical 5 on-wards. The SPOLs of anterior cervical vertebrae convergeon the midline at the spine summit. This morphology createsa prominent postspinal cavity between the SPOLs, whichopens posteriorly and dorsally above the postzygapophyses.


Figure 12 Euhelopus zdanskyi exemplar a (PMU 233). Cervical vertebrae 16 and 17 in right lateral view. See Fig. 7 for abbreviations. Scalebar = 10 cm.

Figure 13 Schematic diagram showing the arrangement of neuralarch laminae and pneumatocoels in cervical (right) and dorsal (left)vertebrae.

There is no evidence that the medial surfaces of the SPOLswere excavated by the three coels observed in the axis. Inmiddle cervical vertebrae, the SPRLs are separate ridges thatextend posterodorsally onto the anterior face of the spine andmerge with each other at the anterior end of the spine summit.These laminae therefore create a triangular prespinal fossa

that is much shallower than the postspinal fossa and flooredby the TPRL.

The lateral profile of the spines also varies along the cer-vical series. In anterior cervical vertebrae, the anterior marginof the spine is relatively steep, whereas the posterior margin,formed by the SPOL, is close to horizontal. This impres-sion is enhanced by the presence of the epipophyses, whichextend the SPOL backwards in lateral view. The SPOLs be-come steeper in the middle cervical vertebrae (e.g. cervical7) and the posterior cervical neural spines have a more sym-metrical triangular lateral profile (Figs 10–12). The summitof the neural spine in anterior cervical vertebrae (cervicals 3–6) is a laterally compressed and anteroposteriorly elongatedridge. Passing along the cervical series posteriorly, this sum-mit region gradually shortens anteroposteriorly and widenstransversely. By cervical 8, the neural spine summit over-hangs the hollow areas on the lateral surfaces of the spine.The neural spines of cervicals 1–10 are unbifurcated and afaint midline notch first appears in cervical 11. From cer-vical 12 onwards, the neural spine is shallowly bifurcated(i.e. its depth does not exceed 50 mm). In all bifurcate neuralspines, the SPRLs are parallel to one another, extending tothe summit of each metapophysis. The base of the notchbetween the metapophyses develops a slight projection incervical 15 and, from cervical 16 onwards into the anteriordorsal vertebrae (see below), a finger-like central projectionis positioned between the metapophyses. This central pro-cess is as tall as the metapophyses themselves in cervical17 and anterior dorsal vertebrae, so that the spine becomeseffectively “trifid” (Fig. 15). This condition is also present inHudiesaurus, from the Late Jurassic of China (Dong 1997).


Figure 14 Camellate pneumaticity in dorsal vertebrae of Euhelopus zdanskyi exemplar a (PMU 233) and exemplar b (PMU 234). Scalebars = 2 cm.

Figure 15 Euhelopus zdanskyi exemplar a (PMU 233). ‘Trifid’ neuralspine in anterior dorsal vertebrae composed of paired metapophyses(mp) and a median tubercle (mt). These correspond to the ‘processuspseudospinosus’ and ‘neuropophysis’, respectively, of Wiman (1929).See Supplementary Data Fig. 1 for comparison. Scale bar = 2 cm.

Below the notch, the wall of bone between the prespinal andpostspinal fossae becomes anteroposteriorly thinner in themost posterior cervical vertebrae. Thus, in cervical 16 thiswall is relatively thin (a few mm) in its middle and ventralregions. In cervical 17, the anterior face of this wall (i.e. theposterior surface of the prespinal fossa) develops a rugosemidline ridge suggesting the attachment of a sheet-like ten-don or aponeurosis.

Cervical ribs (Figs 9–12; Supplementary DataFig. 3)

Ribs are not preserved on the axis or cervical 3, but are pre-served on cervical 4 and most of the subsequent cervicalvertebrae. Their absence on these anterior vertebrae suggeststhat they were not fused; whereas they are fused to all sub-sequent cervical vertebrae. The distal ends of the rib shaftsare broken in cervical 4, but the majority of other ribs arewell preserved and nearly complete. Broken sections in othercervical ribs (e.g. cervical 9) reveal a camellate internal struc-ture.

The cervical ribs of Euhelopus resemble those of othersauropods in that they are double-headed, fused to the ver-tebrae, have short anterior processes and much longer distalshafts. The angle between the tuberculum and capitulum inanterior view is acute, so that the parapophysis–capitulumregion is directed laterally and strongly ventrally. As a res-ult, the rib shafts lie well below the ventral surface of eachcentrum, which represents a derived condition found in neo-sauropods and closely related forms such as Omeisaurus(Wilson & Sereno 1998).

The best preserved middle and posterior cervical tuber-cula display an autapomorphic zigzag profile in lateral view(see Figs 9 & 11). This morphology is created by posteriorly-directed costal spurs at the point where the diapophysis meetsthe tuberculum and more ventrally on the anterior margin ofthe tuberculum (above the anterior process of the rib).

In cervical 4, the anterior process of the rib is longand pointed, and it flattens dorsoventrally towards its tip. In


Figure 16 Euhelopus zdanskyi exemplar a (PMU 233). Dorsal vertebrae 2–5 in right lateral view. See Fig. 7 for abbreviations. Scale bar = 10 cm.

more posterior cervical vertebrae (e.g. cervical 13), the an-terior rib process is prominent, with a subtriangular trans-verse cross-section and a long, triangular outline in lat-eral view. The dorsal edge of the triangular transversecross-section extends posteriorly to the medial margin ofthe anterior rib process and then merges with the anter-oventral edge of the parapophysis. In the rib of cervical15, the base of the anterior rib process becomes trough-like dorsally because of a ridge on the lateral marginfrom the tuberculum and similar ridge on the medial sidefrom the capitulum. Towards its tip the process becomesflattened transversely to form a thin plate. Similar ridgesalso create a trough-like excavation in the base of the distalshaft.

The distal shafts are long and very slender and projectwell beyond the posterior end of the centrum to which therib attaches, as occurs in most sauropods except diplodoc-oids (Wilson 2002; Upchurch et al. 2004a; Sereno et al.2007). Although these distal shafts overlap each other, thearrangement in Euhelopus more closely resembles that ofCamarasaurus than that of Mamenchisaurus hochuanensis,which has extremely long distal shafts that form overlappingbundles of three to five ribs (Young & Zhao 1972). Whereasribs of anterior cervical vertebrae underlap only the vertebraimmediately succeeding them, those of posterior cervicalvertebrae underlap the succeeding two vertebrae. In anteriorcervical vertebrae (e.g. cervicals 4–6), the distal end of therib shaft develops a very thin medial sheet of bone. Thus,although the shaft narrows dorsoventrally in lateral view, itexpands transversely towards its tip. In middle and posteriorcervical ribs the distal shafts taper to very narrow, delicatetips. Cervical 16 has a rib resembling those of the preced-ing vertebrae, whereas in cervical 17 the rib is broader anddirected posteroventrally. This change in rib morphology in-dicates the transition from cervical to dorsal vertebrae (seebelow).

Dorsal vertebrae (Figs 13–20; Supplementary DataFigs 3, 4)

Dorsal vertebrae are defined as having a connection to thesternum via ribs, which enclose the thoracic cavity (Stan-nius 1846). In sauropods, dorsal ribs are free, double-headedand project ventrally. They differ from cervical ribs, whichare fused to the cervical centra and directed parallel to thevertebral axis. As discussed above and in the following de-scription, the cervicodorsal transition is not sharp in Euhel-opus, but extends across at least two vertebrae. We identifiedmore “dorsal characteristics” than “cervical characteristics”in presacral 18 and refer to it as a dorsal rather than a cervicalvertebra, but there remains ambiguity in the actual position ofthe cervicodorsal transition. This ambiguity may seem sur-prising, given that Euhelopus is represented by a completeseries of presacral vertebrae, but the absence of transitionalcervicodorsal ribs prevents us from using the Stannius (1846)criterion to identify the cervicodorsal transition point. Fur-thermore, the distinction between cervical and dorsal verteb-rae can be difficult to make even in living forms for whichsoft tissues are known (e.g. Giraffa; Solounias 1999).

All dorsal centra are opisthocoelous and all bear largepneumatic fossae (i.e. pleurocoels) that are undivided. Thedorsal series displays regional heterogeneity and can besubdivided into “anterior” dorsal vertebrae and “posterior”dorsal vertebrae. Differences in the position and morphologyof the centrum, costal articulations, neural spine and externalpneumatic structures identify the first four dorsal vertebrae asanterior dorsal vertebrae and the succeeding nine vertebraeas posterior dorsal vertebrae. Anterior and posterior dorsalvertebrae are known from exemplar a; exemplar b consistssolely of posterior dorsal vertebrae.

ANTERIOR DORSAL VERTEBRAE (Figs 13, 15, 16;Supplementary Data Figs 3, 4). The first four dorsal


Figure 17 Euhelopus zdanskyi exemplar a (PMU 233). Dorsalvertebra 6 in right lateral view. Dorsal vertebra 7 has been shadowedand a sketch map of vertebral laminae has been overlain upon it. Notethe characteristic “K” laminae formed by diapophyseal andparapophyseal laminae on the lateral aspect of the neural arch (seethe text and Fig. 18 for explanation). See Fig. 7 for abbreviations. Scalebar = 10 cm.

vertebrae retain the sharply-defined dorsal margin of thepleurocoel present in cervical centra, although the pleuro-coels are not divided by an oblique strut. The centra are not-ably stouter than those of the succeeding posterior dorsal ver-tebrae. The anterior dorsal parapophyses are located on thecentrum rather than the neural arch, and the diapophyses arepositioned adjacent to the prezygapophyses (i.e. positionednear the intervertebral foramen). The prezygapophyses arerelatively large and the infradiapophyseal lamination is rel-atively simple. The neural spine is short and does not projectbeyond the plane of the zygapophyses. It bears a rudiment-ary bifurcation and the paired metapophyses are flatteneddorsally.

Dorsal 1 bears characteristics of both the cervical anddorsal regions. Its centrum is as broad as the posterior cervicalcentra that precede it, but notably shorter anteroposteriorly(Table 2). Like cervical parapophyses, those of dorsal 1 hangbelow the ventral aspect of the centrum. The parapophysesare not well preserved but they appear to be complete, sug-gesting that ribs were not fused to them, which is typical ofthe dorsal series. However, we do not know whether dorsalrib 1 was orientated parallel to the vertebral column (as inthe cervical series), perpendicular to it with a contact to thesternum (as in the dorsal series), or was intermediate in mor-phology. As in the last cervical centrum, the pleurocoel ofdorsal 1 is not divided. The centrum bears a ventral hollowwith a narrow median strut. The diapophyses, which pro-

Figure 18 Euhelopus zdanskyi exemplar a (PMU 233). Close up ofneural spine of dorsal vertebra 7 in right lateral view to show verticaldivision of pneumatic coels (1v, 2v) by the spinodiapophyseal lamina(spdl). See Fig. 7 for other abbreviations. Scale bar = 5 cm.

ject toward the anterior margin of the centrum, are pendantand hang down near the level of the pleurocoel. They beara flattened lateral surface that is also present on the anteriordorsal vertebrae that follow it. The configuration of diapo-physeal laminae changes dramatically over the course of theanterior dorsal vertebrae. In dorsal 1, as in the cervical ver-tebrae, the diapophysis hangs below the level of the zygapo-physes. Consequently, laminae joining the diapophysis andthe zygapophyses (PRDL, PODL) have a dorsal componentto their orientation, and the PCDL is nearly horizontally ori-entated. As in the posterior cervical vertebrae, the remnantof the EPRL partially divides the lateral aspect of the meta-pophysis horizontally into two pneumatic fossae, the upperlabelled “1h” and the lower labelled “2h” (see Figs 13, 17 &18). Pneumatic fossa “3” is present and positioned betweenthe centropostzygapophyseal, posterior centrodiapophysealand postzygodiapophyseal laminae (see Fig. 13). Pneumaticfossa “1h” is the smallest, due to the relatively short neuralspine that rises only slightly above the level of the postzy-gapophyses. The neural spine is incipiently bifurcated andbears a small median tubercle between its metapophyses.

The remaining anterior dorsal vertebrae will bedescribed together. Dorsal centra 2–4 are approximately thesame length and only slightly shorter than dorsal 1. They areall notably broader than those of the posterior dorsal verteb-rae that follow (see Table 2). Progressing posteriorly fromdorsal 1 to dorsal 4, the parapophysis changes in shape andposition. In dorsal 1 it is circular and positioned near the vent-ral centrum, whereas in dorsal 4 it is elliptical and straddlesthe neurocentral junction. In intervening dorsal centra theparapophysis is of intermediate morphology and position;in dorsal 2 it is circular and positioned at the anteroventral


Figure 19 Euhelopus zdanskyi exemplar b (PMU 234). Dorsal vertebrae 5–11 in right lateral view. See Fig. 7 for abbreviations. Scale bar = 10 cm.

corner of the pleurocoel (Fig. 16), and in dorsal 3 it iselliptical and located on the anterodorsal corner of the pleur-ocoel. In all four anterior dorsal vertebrae, the diapophysisextends forward to the level of the preceding vertebra andprojects laterally further than do the cervical or posteriordorsal diapophyses. The neural arch lamination also changessubstantially between dorsals 1 and 3. In dorsals 1 and 2, asin the posterior cervical vertebrae, the EPRL is an isolated,horizontally-orientated strut that divides the lateral aspectof the metapophysis into upper and lower pneumatic fossae(Fig. 13; Supplementary Data Fig. 3). This strut disappearsin dorsal 3 and is replaced by the spinodiapophyseal lamina(SPDL). There is no vertebrae in which both lamina arepresent. This vertically orientated strut divides the lateralaspect of the metapophysis into two pneumatic fossae. Thus,a pattern of three pneumatic fossae is retained in this and theremaining dorsal vertebrae, but they are orientated differ-ently and bounded by different laminae (Fig. 13). Whereasin the cervical and anteriormost dorsal neural arches, ahorizontal lamina (EPRL) divides the metapophyseal spaceinto upper and lower pneumatic fossae, in all succeeding ver-tebrae a vertical lamina (SPDL) divides the metapophysealspace into fore and aft pneumatic fossae. The position andbounding laminae of pneumatic fossa 3 does not vary alongthe presacral vertebral column. The neural spine remainsrelatively low and incipiently divided in dorsals 2–4 (seeFig. 20). A roughened, flattened region is present on thedorsal surface of the metapophyses, between which emergesan elongate median tubercle. In anterior or posterior view, theneural spine has a “trifid” appearance (see Fig. 19). These an-terior dorsal vertebrae may serve as the site of attachment ofnuchal ligaments that extend down the neck (Tsuihiji 2004).

POSTERIOR DORSAL VERTEBRAE (Figs 13, 14, 17–20; Sup-plementary Data Figs 3, 4). The remaining dorsal vertebraecan be readily distinguished from anterior dorsal vertebraeon the basis of many features. The centrum is notably nar-rower (though not shorter) than those of the preceding verteb-

Figure 20 Schematic diagram showing the arrangement ofparapophyseal and diapophyseal laminae of dorsal vertebrae to form“K” laminae (bold lines). See Figs 15 and 17 for comparison. See Fig. 7for abbreviations.

rae (see Table 2) and the pleurocoel is not sharply boundeddorsally. Unlike the condition in the anterior dorsal verteb-rae, the diapophysis does not extend forward level with theintervertebral space, but rather is positioned at mid-centrum.The parapophysis, however, is positioned level with theintervertebral space. A cross-pattern of “K” laminae can be


recognised on the lateral aspect of the neural arch, a featurethat may be diagnostic of Euhelopus (Fig. 17). The neuralspine is elongate and more deeply bifurcate; the metapo-physes are more broadly separated.

Exemplar a includes both anterior and posterior dorsalvertebrae, whereas exemplar b and exemplar c consist solelyof posterior dorsal vertebrae. The posteriormost preservedportion of exemplar a includes a series of posterior dorsal ver-tebrae (dorsals 5–8) that is continued in exemplar c (dorsals8–11). The first preserved vertebra of exemplar b correspondsto presacral 22 (dorsal 4), as suggested by Wiman (1929) inhis original description, and the uninterrupted series contin-ues through the sacrum. The centra of dorsals 5 and 6 aremore elongate and transversely narrow than the precedingvertebrae, but it is not known whether this trend continuesposteriorly, because dorsal 7 is damaged ventrally, and trans-verse measurements are not available for dorsals 8–11 onexemplar c. In dorsals 5–10, the diapophysis is positionedabove mid-centrum or over its posterior half, and the PCDLis orientated subvertically. Along the transition marked bythese same dorsal vertebrae, the parapophysis becomes elev-ated and anteriorly shifted to a position adjacent to the prezy-gapophysis and it extends into the intervertebral space. Thedifference in relative anteroposterior positions of the costalarticulations must reflect a difference in the orientation and/orshape of the ribs, but only one dorsal rib is preserved (seeFig. 2). Despite its elevation on the neural arch, the para-pophysis in posterior dorsal vertebrae is always positionedlower than the diapophysis, and the paradiapophyseal lamina(PPDL) – which first appears in dorsal 5 – is orientated anter-oventrally. The PPDL parallels the PRDL and, together withthe diapophysis and prezygoparapophyseal lamina (PRPL),they define the boundaries of an elongate coel that is vis-ible in lateral view (see Figs 17 & 19). Both the diapophysisand the parapophysis of posterior dorsal neural arches aresupported by laminae that extend anteriorly and posteriorlytowards the centrum. These laminae intersect to form a char-acteristic cross pattern of “K” laminae in dorsal 5 and allmore posterior dorsal vertebrae in both exemplar a and ex-emplar b (see Figs 17 & 19). The identities of the laminaethat comprise the “K” laminae is not obvious, but we providean interpretation in Fig. 20. The vertical portion of the “K”is formed by the PCDL, which can be unambiguously iden-tified on the basis of its connections to the diapophysis andthe posterior portion of the centrum. The upper arm of the“K” is most parsimoniously interpreted as the PCPL, onthe basis of its clear connection to the parapophysis andits contact to the PCDL near the posterior portion of thecentrum. The lower, short arm of the “K” contacts the PCPLposterodorsally and extends anteriorly towards the centrum.Although it does not have a direct connection to the diapo-physis, we interpret this to be the ACDL. If this interpretationis correct, it suggests that the ACDL drops out of the dorsalseries when the parapophysis is in an intermediate positionon the neural arch (replaced by the PPDL and ACPL; Wilson1999), but then reappears once the parapophysis approachesthe level of the prezygapophysis in more posterior dorsalvertebrae. An alternative is to consider the lower, short armof the “K” to be a novel lamina (e.g. accessory posteriorcentrodiapophyseal lamina), as Salgado et al. (2005) did intheir description of Neuquensaurus. Whilst we admit someuncertainty in our interpretation, we consider it more con-servative to identify existing laminae before defining newones.

Figure 21 Euhelopus zdanskyi exemplar a (PMU 233). Dorsal rib inposterior view showing pneumatic coel (co). Scale bar = 5 cm.

The height of the dorsal neural spines increases posteri-orly through the posterior dorsal series. The anteroposteriorexpanse of the neural spine increases abruptly between an-terior and posterior dorsal vertebrae, but does not continueincreasing posteriorly. The orientation of the SPDL changesbetween anterior and posterior dorsal vertebrae. Whereas indorsal 4 the SPDL is forwardly orientated and is conjoinedwith the PODL near the diapophysis, the SPDL in more pos-terior dorsal neural arches attaches to the posterior face ofthe neural spine and is not conjoined with the PODL. Thismore vertically orientated SPDL divides coels that are sube-qual in area (coels 1v and 2v). More posterior dorsal neuralarches, beginning with dorsal 6, develop triangular lateralprocesses that hang ventrally. These probably served as at-tachment sites for epaxial musculature of the neck, as they doin birds (Wedel & Sanders 2002: Table 2), but their functionalsignificance has not been examined.

Dorsal ribs (Fig. 21; Supplementary Data Fig. 3)

Only a single dorsal rib, which Wiman (1929:17) identifiedas the left rib of dorsal 3, was preserved with exemplar a.Wiman’s illustration of that rib (1929: pl. 3, fig. 19) did notdraw attention to the large coel that opens on the tuburcu-lar portion of the proximal rib head (Fig. 21). The internalstructure of the rib is not known, but pneumaticity extendsthrough approximately two-thirds of the rib length in othertitanosauriform sauropods, such as Brachiosaurus (Wilson2002). Right ribs were preserved in articulation with the lasttwo dorsal vertebrae in exemplar b. These two ribs contacteach other and the anterior aspect of the first sacral rib, whichis attached to the dorsal surface of the preacetabular processof the ilium (Supplementary Data Fig. 4).

Sacral vertebrae (Figs 22, 23; Supplementary DataFig. 4)

The sacrum has not been completely prepared and remainsmounted in the PMU exhibit hall as it was during Wiman’stime (see Fig. 5). Matrix remains between the sacrum andilium, and only the lateral aspect of the neural spines and


Figure 22 Photograph of PMU technician Nils Hjort preparing thesacrum of Euhelopus in the mid 1920s. This is one of the few knownphotographs that shows the dorsal aspect of the sacrum, which canno longer be viewed due to the enclosure in which it is stored in (seeFig. 5). Photograph kindly provided by Museum of Evolution, UppsalaUniversity.

diapophyses and the posterior aspect of the last sacra verteb-ral are visible. Accordingly, our description of sacral mor-phology is based on those visible parts, figures from Wiman(1929: pl. 4, figs 1–5) and early photographs (Fig. 22).

Although the ribs of the 29th and 30th presacral ver-tebrae indirectly contact the ilium via the rib of the 31stvertebra, we do not consider them to be sacral vertebraebecause they do not directly contact the ilium. Only thosevertebrae whose ribs contact the sacrum and are thus directlyinvolved in connecting the hindlimb to the axial column arehere considered sacral vertebrae. Following this definition(e.g. Romer 1956), Euhelopus has six sacral vertebrae, thefirst of which is connected to the ilium via an elongate ribthat contacts the preacetabular process. A similar conditionis present in a specimen referred to Camarasaurus (BYU17465; Tidwell et al. 2005), in which a sixth sacral ver-tebra has been added anteriorly. In this latter specimen, thepresumptive first sacral rib appears to contact the ilium justanterior to the succeeding rib on the right side; the conditionon the left side is more difficult to discern. Most Camara-saurus specimens have five sacral vertebrae and the conditionin BYU 17465 was regarded by Tidwell et al. (2005) as age-related. Euhelopus exemplar b appears to be at an earlierstage of ontogeny, as evidenced by traces of neurocentral su-tures visible on all dorsal vertebrae, so the additional sacralvertebra cannot be attributed to old age.

The first and second sacral vertebrae of Euhelopus re-tain the camellate pneumaticity present in the dorsal series;the last sacral appears to lack camellate pneumaticity as thecaudal vertebrae presumably would. Nevertheless, the sixthsacral centrum bears a pleurocoel-like depression on its lat-eral surface and was probably pneumatised, if only partially(Fig. 23). The transition between the dorsal-like pneumati-city of the anterior sacrum and the reduced pneumaticity inthe posterior sacrum cannot be assessed in its current state

Figure 23 Euhelopus zdanskyi exemplar b (PMU 234). Sacralvertebra 6 in left ventrolateral view. Abbreviations: ct, cotyle; il, ilium;is, ischium; pc, pleurocoel; sr, sacral rib. Scale bar = 5 cm.

of preparation. It would be interesting to know whether theintervening vertebrae, which represent primordial sacral orcaudosacral vertebrae, resembled the sixth sacral more thanthe anterior, dorsosacral vertebrae.

The presence and extent of the sacricostal yoke couldnot be assessed due to the matrix filling the pelvic basin.However, it is likely that Euhelopus had a sacricostal yokethat formed part of the articular surface of the acetabulum.

Scapula, coracoid and humerus (SupplementaryData Fig. 5)

Young (1935) described a left scapula, coracoid and humerusfrom what may be the same quarry as exemplar a. The loca-tion, size, lack of duplication of these elements and Young’sconviction all suggest that exemplar a and c represent oneindividual. Unfortunately, the whereabouts of exemplar cis unknown, and we were not able to examine it directly.Our description of these elements herein will be accordinglybrief and will focus on salient features gleaned from Young(1935).

The scapula and coracoid were articulated, and the hu-merus was found only 1 metre away. The scapula is an elong-ate element (1.2 m long) that bears a deep acromion and anarrow blade. The axis of the scapular blade passes throughthe coracoid articulation but not the glenoid, which appearsto face medially (Young 1935: fig. 2). The neck of the bladeis quite narrow and it expands dorsally and ventrally. A pro-nounced muscle scar appears at the ventral margin of thebase of the blade. The position of the scar near the glen-oid corresponds to the origin of the triceps longus lateralismuscle in extant crocodylians (Meers 2003). The blade isquite thin and its cross-section is nearly flat. This differsfrom the D-shaped expansion of the scapular blade found inCamarasaurus. There is no asymmetrical dorsal expansionnor thickening of the base of the blade such as that seen inCamarasaurus. The coracoid is about half the dorsoventralheight of the base of the scapula. The coracoid portion ofthe glenoid is smaller than that of the scapula, and it faceslaterally (Young 1935: fig. 4).


The humerus, like the scapula, is slender and elongate(length = 91 cm). It is strongly expanded proximally but lessexpanded distally; their maximum transverse diameters are36.3 cm and 22.5 cm, respectively. At midshaft, the humerusnarrows to only 17.5 cm, which is approximately half thebreadth of the proximal end. If exemplars a and c pertainto the same animal, as suggested here and elsewhere (Young1935; Mateer & McIntosh 1985), then a high humerus–femurratio is implied. However, owing to the incompleteness ofproximal and distal ends, the length of the exemplar a femurreported by Wiman (1929; Table 2) is a minimum value.Consequently, the estimate of 0.99 provided by Mateer &McIntosh (1985:129) may be may be too high.

Pelvis (Figs 22, 24, Supplementary data Fig. 4)

Both left and right halves of the pelvis are preserved in ar-ticulation with the vertebral column in exemplar b (PMU234; Figs 3, 5 & Supplementary Data Fig. 4). Matrix wasnot removed from the space enclosed by the pelvis and,consequently, only external features of the pelvis are ex-posed. Unfortunately, due to the constraints of the enclosurein which it is mounted (see Fig. 5), the dorsal aspect ofexemplar b cannot be adequately viewed. As visible in pos-terior, lateral and dorsal views (Fig. 22, Supplementary DataFig. 4), the left side of the pelvis has been sheared relative tothe right ventrally by 5–12◦ and anteriorly by 7–12◦. Despitethis shearing, the relative orientation of the ilia with respectto the vertebral axis appears to be the same on both sides ofthe pelvis – the chord passing through the base of the pubicand ischial peduncles forms a 42◦ angle with the vertebralaxis.

The right and left ilia are well preserved, but both aremissing the anterior tip of the preacetabular process, and theleft ilium is missing the posterior portion of the blade. Theiliac blade is semicircular to crescent-shaped in lateral view.The preacetabular process of the blade extends laterally at a45◦ angle to the vertebral axis, as in other non-titanosaurianneosauropods (see Wiman 1929: pl. 4, fig. 3). The brokensurface of the right ilium exposes large cells that were prob-ably air-filled pneumatic spaces (Fig. 24). Closer examin-ation reveals similar evidence of pneumaticity on the leftilium. Unfortunately, it was not possible to determine theextent of pneumaticity within the ilium or the source of thepneumatisation (i.e. a pneumatic foramen on medial aspectof ilium) because of the inaccessibility of the pelvic basin.Wiman (1929:23) noted this feature, stating “With exceptionof the acetabular margin, the whole ilium is very cavernous,provided with somewhat larger cavities than the vertebrae.The two other pelvic elements, in contrast, are completelysolid.” Camellate pneumaticity extending into the ilium isalso known in the titanosaurs Epachthosaurus (Martınezet al. 2004), Lirainosaurus (Sanz et al. 1999) and Sonido-saurus (Xu et al. 2006) and was reported in a sauropod fromthe Dry Mesa Quarry of the western US (Britt 1993:188). Thepubic peduncle projects orthogonally to the vertebral axis andis positioned on the posterior half of the iliac blade; its lengthis subequal to the maximum height of the iliac blade. Thepubic peduncle is more than twice as broad transversely as itis anteroposteriorly. The ischial peduncle is relatively smalland does not project much beyond the iliac blade.

The right pubis is nearly complete, lacking only part ofthe iliac peduncle. The left pubis is much more incomplete,

Figure 24 Euhelopus zdanskyi exemplar b (PMU 234). Detail of rightiliac blade indicating appendicular pneumaticity in the form of largecamellae. Scale bar = 5 cm.

but the proximal portion is well preserved. Like the pubicpeduncle of the ilium, the iliac peduncle of the pubis is muchbroader transversely than anteroposteriorly. As in other saur-opods, the pubes meet along an elongate symphysis that isorientated subvertically. The pubic contribution to the acet-abulum is smaller than the ischial contribution, in part owingto the enlarged contribution of the pubic peduncle of theilium.

The right ischium is more completely preserved than theleft, which lacks a blade. The ischium is shorter than the pu-bis, as it is in most titanosaurs (Wilson 2002), and the distalblades meet along a narrow edge to form a midline sym-physis. The blades are orientated subhorizontally, as in othermacronarians and rebbachisaurids (Upchurch 1998; Wilson& Sereno 1998; Wilson 2002; Upchurch et al. 2004a). Asmall boss is located on the proximolateral surface of theischium, as in Brachiosaurus (Janensch 1950; MB J3).

Hindlimb (Fig. 25; Supplementary Data Fig. 4)

The right hindlimb of exemplar b is nearly complete, lackingonly a few pedal phalanges. It is mounted in articulation,which limits observations that can be made on the mutualarticular surfaces of the tibia and fibula. The astragalus hasnot been separated from the tibia, so their articular surfaceslikewise cannot be viewed.

Femora are present in both exemplar a and exemplarb. The latter is more completely preserved than the former,which lacks a head and tibial condyle. Although no signific-ant differences were observed between the two elements, noautapomorphies were identified that specifically link them.

FEMUR. The femur is fairly straight in anterior view butbears a sharp deflection in its proximal third, as in other


Figure 25 Distal hindlimb of Euhelopus zdanskyi exemplar b (PMU234) in anterior (left) and oblique proximal (right) views.Abbreviations: ac, anterior crest; cc, cnemial crest; fc, fibular condyle;fe, femur; fi, fibula; tc, tibial crest; ti, tibia. Scale bar = 10 cm.

titanosauriforms (Supplementary Data Fig. 4; Salgado et al.1997). As in other sauropods, the femoral shaft in Euhel-opus is anteroposteriorly compressed. In cross-section its me-diolateral axis is 160% its anteroposterior axis, which is not aseccentric as in some titanosaurs (>185%: Wilson & Carrano1999). The distal condyles of the femur are slightly beveledmediodistally (ca. 4◦; Fig. 25), as in Gobititan (Youet al. 2003: fig. 2) and some diplodocids (e.g. Apatosaurus;Upchurch et al. 2004b: pl. 9).

CRUS. The tibia and fibula are approximately 68% the lengthof the femur. The tibia and fibula interlock proximally in afashion that has not yet been described in other sauropods butappears to be common in titanosauriforms. The cnemial crestof the tibia is orientated laterally, as in other sauropods, andoverlaps the anterior aspect of the fibula. The fibula, in turn,has an anterior crest that extends medially into a notch be-hind the cnemial crest and is sandwiched between it and thebody of the tibia (Fig. 25). This mutually overlapping rela-

Table 3 Measurements (cm) of the tarsal elements ofEuhelopus zdanskyi (PMU 234).

Element Dimension cm

Astragalus Transverse width 15.2Anteroposterior width across lateral surface 10.3Height of lateral surface (including

ascending process)9.4

Calcaneum Maximum diameter 6.1Maximum proximodistal thickness 4.1

tionship between proximal tibia and fibula is present in othertitanosauriforms such as Erketu (IGM 100/1803), Gobititan(You et al. 2003: fig. 3), Tangvayosaurus (J.A.W., pers. obs.,2008), possibly Magyarosaurus (BMNH R 3853), and thetitanosaur from Chota Simla, India described by Swinton(1947).

TARSUS. The astragalus is interlocked with the distal tibiaand fibula, and it can only be viewed anteriorly, posteriorlyand medially. This element is as broad transversely as isthe distal tibia, which is the symplesiomorphic condition forsauropods. The astragalus does not reach the medial marginof the tibia in other Cretaceous Asian titanosauriforms, suchas Gobititan (You et al. 2003: fig. 2), Erketu (Ksepka & Norell2006: fig. 10) and Opisthocoelicaudia (Borsuk-Bialynicka1977: pl. 14, fig. 2b). In proximal and distal views, the as-tragalus is subtriangular and tapers to an acute but roundedmedial corner. The astragalus also tapers proximodistally to-wards this corner, so that this part of the element is relativelyslender (Table 3). It is not possible to determine the number ofridges and hollows on the posterior surface of the astragalus.The rugose distal surface is convex transversely and stronglyrounded anteroposteriorly. As in all sauropods more derivedthan Vulcanodon (Wilson & Sereno 1998), the anterior sur-face of the astragalus lacks a fossa containing foramina atthe base of the ascending process. In fact, the anterior faceof this process and the anterior face of the rest of the boneare continuous with no obvious demarcation between them.The lateral end of the astragalus is shallowly concave andfaces laterally and slightly posteriorly. There is no distal lipprojecting laterally under the fibula. In the posterodorsal partof this surface, there is a small, deep hollow that does notappear to be the result of damage.

As mounted, there is a distinct gap between the distalend of the fibula and the proximal ends of the metatarsals.Wiman (1929:25–26) described only one tarsal element, buta bone he identified as the ungual phalanx of digit III isprobably the calcaneum (see Fig. 4; Supplementary data Fig.4; see also Wilson & Sereno 1998). The calcaneum of Eu-helopus is a proximodistally compressed lump of bone thatis relatively smooth on its proximal and distal surfaces andrugose on its anterior, posterior, lateral and medial faces(Fig. 26). In proximal view, the calcaneum has a sub-circular outline, while in anterior view it is compressedmediolaterally. In these respects, the calcaneum of Euhel-opus resembles those of Gobititan (You et al. 2003; P.U.,pers. obs., 2007), Erketu (Ksepka & Norell 2006), Camara-saurus and Diplodocus (Bonnan 2000), and differs from themore globular calcanea of Brachiosaurus and Lapparento-saurus, which have a more subrectangular proximal outline(McIntosh 1990). The Euhelopus calcaneum has its greatest


Figure 26 Euhelopus zdanskyi exemplar b (PMU 234). Rightcalcaneum in lateral (A), medial (B), and anterior (C) views, withproximal towards top. Scale bar = 5 cm.

proximodistal thickness near its lateral margin, so that theproximal articular face slopes slightly mediodistally. Oneslight anomaly is that the proximal articular surface of thecalcaneum in Euhelopus is flat anteroposteriorly and convextransversely and therefore lacks the slight concavity foundin the calcanea of most other sauropods (McIntosh 1990;Bonnan 2000). The distal articular surface is strongly convexanteroposteriorly and slightly convex transversely, as is alsoseen in the calcaneum of Gobititan (P.U., pers. obs., 2007).

PES. The pes includes four metatarsals and severalphalanges, none of which were found in articulation andwere reconstructed by Wiman (1929:21) in a manner that was“completely arbitrary in several ways” (see SupplementaryData Fig. 4). As discussed below, we suggest several reiden-tifications and reorientations for pedal elements based oncomparisons with articulated sauropod hind feet.

In Wiman’s reconstruction and in the skeletal mount,metatarsal I is orientated upside-down (NB: this orientation

was corrected by the authors while in Uppsala). This elementhas the typical short, robust morphology seen in other eusaur-opods (Upchurch 1998; Wilson & Sereno 1998; Upchurchet al. 2004a). The profile of the proximal end is more subtri-angular than D-shaped: there is a long, curving dorsomedialmargin, a short, straight ventral margin (facing slightly lat-erally), and an intermediate length, straight margin facinglaterally and a little downwards. Thus there is a more acuteventromedial corner to the proximal end profile than in othersauropods. The proximal articular surface itself is mildlyconcave over most of its extent, occupying an elliptical areaover the central and medial regions of the surface. Towardsthe ventrolateral corner and ventral margin, this surface be-comes mildly convex and slopes strongly distally, so that itdoes not take part in the true articular surface. The proximaland middle portions of the lateral side of the shaft form theusual triangular striated shallow excavated area seen in othersauropods. This area is bounded dorsally by an acute marginwhere the dorsal and lateral surfaces meet. At approximatelytwo-thirds of the length of the bone from the proximal end, asthe dorsal and ventral surfaces converge towards each other,the anterior tip of the lateral triangular excavation ends in amild projection. This projection lies on the posterior marginof a shallow, subcircular excavation on the side of the lateraldistal condyle. The dorsal surface of the shaft is nearly flattransversely and mildly concave anteroposteriorly (becauseof the expansion of the proximal end). There is no rugos-ity on the dorsolateral margins of the shafts of metatarsalsI–III. Thus Euhelopus lacks the derived state observed inthe pedes of diplodocids (Upchurch 1998; Upchurch et al.2004a). The stout shaft of the bone is thickest dorsoventrallyon its medial side, so that the dorsal surface slopes down-wards as it extends laterally. Medially, the side of the shaftis strongly convex dorsoventrally and merges smoothly intoboth the dorsal and ventral surfaces. The ventral surface isgenerally mildly convex transversely and concave antero-posteriorly, again because of the expansion of the proximaland distal ends. The distal end is expanded both transverselyand dorsoventrally (particularly the medial condyle whichis noticeably deeper than the lateral one because of a milddorsal projection). In Euhelopus, the distolateral condyle ofmetatarsal I lacks the ventral process seen in diplodocids,Brachiosaurus and Omeisaurus (McIntosh et al. 1992; X.He et al. 1988). The distal end surface is convex dorsovent-rally and straight or slightly concave transversely. In dorsalview, the lateral distal condyle projects further distally, sothat the bone is longer on its lateral margin than its medialone. There are no distinct selvages (i.e. shelf-like ridges ofbone) around the distal condyles, especially the medial onewhich completely lacks any excavation on its medial sur-face: instead this area is mildly convex both dorsoventrallyand anteroposteriorly.

The proximal end of metatarsal II has a subrectangularoutline, with the long axis running downwards and a littlemedially. The dorsal part of this surface is slightly expan-ded medially and laterally so that these areas overhang themedial and lateral surfaces. The ventral margin is mildlyrounded transversely. The proximal articular surface is flatbut is slightly convex in places because of irregular projec-tions, particularly on the lateral margin about one-third ofthe way down from the dorsal margin. Dorsally, the shaft’ssurface is flat transversely on the proximal part and becomesvery slightly convex distally. There is no distinct transverse


Table 4 Measurements (in cm) of the pedal elements of Euhelopus zdanskyi (PMU 234).

Dimension Mt I Mt II Mt III Mt IV Ph II.1 Ph III.1 Ph IV.1 Ph I.2 Ph II.3

Length of lateral side 9.8 12.2 13.6 12.1 4.3 4.0 2.8 12.4 10.9Length of medial side 8.8 10.8 12.4 12.0 4.5 3.9 3.3 — —Height of proximal end 7.8 7.7 6.6 6.1 4.0 3.8 3.0 7.2 8.7Maximum width of proximal end 6.7 5.2 4.2 4.5 6.4 5.4 5.6 4.7 3.8Minimum transverse width of shaft

(viewed dorsally)6.1 4.3 2.9 2.8 — — — — —

Transverse width of distal end 8.0 6.4 5.4 5.4 3.8 3.3 2.8 — —Maximum height of distal end

(medial condyle)4.7 4.2 4.1 3.2 6.4 4.7 5.5 — —

ridge where the proximal and dorsal surfaces meet, nor dothe proximal medial and lateral corners form distinct pointsor projections. The lateral surface has the usual slightly con-cave triangular area near the proximal end, but this is onlyweakly developed. The medial surface near the proximal endis also slightly concave, but this is an impression exagger-ated by a bulge-like area on the lower part of the medialsurface. In transverse cross-section, the shaft has a subcir-cular outline, being slightly compressed dorsoventrally andforming a sharper angle where the dorsal and lateral marginsmeet (all other surfaces merge smoothly into each other).The distal end expands both dorsoventrally and transversely.As in metatarsal I the medial condyle is thicker dorsovent-rally, whereas the lateral condyle projects more outwardlyand distally. Consequently, the element is longer on its lat-eral side so that the distal end surface lies at an angle tothe long axis of the shaft. The distal end surface is stronglyconvex dorsoventrally.

Metatarsal III is placed in the mount as metatarsal IV,but we have reidentified it on the basis of its relative lengthand robustness: in the eusauropod pes, digit I is the thickestand the metatarsals become narrower in transverse cross-section towards the lateral extreme of the pes (Wilson &Sereno 1998). In many respects its morphology is interme-diate between metatarsals II and IV. The long axis of theproximal articular end slopes medially and downwards, butnot as strongly as in metatarsal IV. There is a mildly convexarea on the dorsal part of the proximal articular surface. Theproximal part of the medial surface is generally concave overmost of its extent and therefore lacks the bulge-like area ofbone near the ventral margin observed in metatarsals II andIV. In transverse cross-section, the shaft is compressed fromdorsomedially to ventrolaterally, with an oval to ellipticaloutline. The shaft is slender and measurements indicate thatthe minimum shaft widths for metatarsals III and IV are lessthan 65% of those in metatarsals I and II, which is a derivedstate characterising eusauropods (Wilson & Sereno 1998; seeTable 4). Distally, the articular end surface is squarer than inmetatarsal IV with the medial condyle being deeper thanthe lateral one. The medial condyle also has a flat externalsurface rather than the more rounded one seen in metatarsalIV. A distinct ridge marks the boundary between distal andventral surfaces.

Metatarsal IV is positioned in the mount as “meta-tarsal III”, with the proximal and distal ends reversed. Wehave reidentified this element as metatarsal IV because it isshorter and has a less robust shaft than “metatarsal III” (seeabove and Table 4). The main difference between metatarsalsIII and IV is that the long axis of the latter’s proximal end

surface is rotated more strongly relative to that of the distalend. As a result, the long axis of the proximal end surfaceslopes strongly medially and downwards. Both the proximaland distal surfaces slant relative to the long-axis of the shaft,so that the lateral margins lie more distally than the medialmargins. The proximal part of the medial surface bears aconvex area near the ventral margin, creating a shallow con-cavity between it and the dorsomedial margin. In dorsal view,the shaft is narrowest transversely at a point slightly closerto the proximal end than midlength and then widens gradu-ally towards the distal end. The distal articular surface hasan elliptical outline, with rounded lateral and medial marginsrather than straight edges. There is a more distinct break ofslope between the distal and ventral surfaces, but the dorsaland distal surfaces merge smoothly into each other.

Three proximal phalanges are preserved, which havebeen mounted with the metatarsals II–IV. The proximalphalanx of metatarsal I is generally wedge-shaped in saur-opods, and none of the preserved phalanges bear thisform, indicating phalanx I.1 was not preserved (Mateer &McIntosh 1985). Consequently, the three proximal phalangesare probably correctly assigned to the inner three metatars-als. Phalanx II.1 is a subrectangular element in dorsal view,with the long axis orientated transversely. The proximal endand shaft have an oval outline in transverse cross-section,with a thick, rounded medial side and sharper tapered mar-gin where the dorsal and ventral surfaces meet to form thelateral edge. The proximal articular surface is mildly con-vex in its medial part and shallowly concave in its lateralpart, giving it a slightly sigmoidal profile in dorsal view. Thisproximal bulge, combined with the expansion of the medialdistal condyle, make the bone slightly longer on its medialside than on its lateral one. The ventral surface is very mildlyconcave both transversely and anteroposteriorly. Distally, thearticular surface is strongly convex dorsoventrally and mildlysigmoid transversely because of the expansion of the medialdistal condyle. Phalanx III.1 is similar to phalanx II.1, butslightly smaller (see Table 4). The proximal articular surfaceis very mildly concave in all directions. It is subrectangu-lar in dorsal view with the long-axis running transversely. Intransverse cross-section, the shaft is oval and tapers towards asharper lateral margin. The ventral surface is mildly concavein all directions. Compared to phalanx II.1, the distal end isflatter dorsoventrally and is more distinctly separated fromthe ventral and dorsal surfaces. This distal articular surfaceis also more concave transversely. Much of this differenceis caused by the distal convexity of the lateral condyle. Indistal end view, the articular surface is semicircular in out-line, rather than oval, because of the height of the lateral


condyle. Phalanx IV.1 is a small, subrectangular bone that isrelatively wide compared to its anteroposterior length. Theproximal surface is generally irregular and mildly concave.The outlines of the proximal end and shaft transverse cross-section are not oval because there is a small lateral surfacethat faces laterally and ventrally, separating the true ventraland dorsal surfaces. Dorsal and lateral surfaces meet at anacute margin, whereas the dorsal and medial surfaces mergesmoothly into each other. The ventral surface is mildly con-cave. Distally, the articular surface is mildly and irregularlyconvex.

Three elements were described by Wiman (1929) asungual phalanges, and they have been mounted in this posi-tion (Supplementary Data Fig. 4). There was no first phalanxpreserved with digit 1, and its ungual has therefore beenplaced in contact with metatarsal I in the mount. The ele-ment Wiman (1929) identified as the digit 1 ungual has anunusual appearance, and we cannot be certain that it has beenproperly identified (see below). The element appears to havebeen crushed mediolaterally, so that it has an unusually acuteridge extending along its dorsal margin. It is very tall relat-ive to its transverse thickness and there is no sign that theproximal articular surface, which is shallowly convex, slopesat an angle to the long axis of the bone, as it does in neo-sauropods. Therefore, were this element an ungual, it wouldhave been directed forwards, rather than laterally, a featurethat is only retained in basal sauropods. In lateral view, theelement has a strongly curved, hook-like profile comparedto those of other sauropods. The lateral surface is relativelyflat and this surface and the medial surface show no signsof longitudinal nail attachment grooves. The margin wherethe lateral and ventral surfaces meet forms a sharp ridge.Apart from the general side view profile, the most claw-likeaspect of this element is seen on the medial surface. Here,the ventral surface faces downwards and medially, and meetsthe medial surface at a distinct ridge or break of slope, as inother sauropod unguals. This ventromedial surface is wide atthe proximal end but narrows distally to the point where theclaw terminates in a very blunt tip. We consider it uncertainor even unlikely that this element is an ungual, but we canforward no better identification for it at this time.

The element identified as the ungual of digit two bearsthe conventional morphology of sauropod unguals. It is lar-ger than the element Wiman (1929) identified as the digit 1ungual. It is probable that the larger element actually belongsto digit 1, not digit 2. This element is strongly compressedtransversely and the proximal articular surface has an ovaloutline with a rounded, bulging ventral part that narrowsdorsally. There is a distinct nail groove that is asymmetrical,positioned higher on the medial side than on the lateral side.The proximal articular surface is subtly divided into upperand lower regions by a transverse ridge. The upper triangu-lar region faces backwards, whereas the lower more roundedregion faces backwards and downwards. In dorsal view, theproximal articular surface lies at an angle of approximately70◦ to the long axis of the claw, so that it faces proximallyand a little laterally. This suggests that the claw pointed for-wards and laterally when in articulation. The medial surfaceis smooth and mildly convex both dorsoventrally and antero-posteriorly. On the lateral surface of the ungual, there is anail attachment groove on the middle and distal regions atapproximately midheight. The middle and distal parts of theventral margin of the medial surface form a distinct, thin

ridge that is slightly separated from the rest of the ventralsurface. This feature is reminiscent of the more strongly de-veloped ridge in the pedal unguals I–III of Gobititan (P.U.,pers. obs., 2007).

The element described and mounted as the third ungualis actually the calcaneum, as described above.

Discussion

Phylogenetic affinities of Euhelopus

Revised scorings for the Wilson (2002) and Upchurch et al.(2004a) matrices are presented in Tables 5 and 6. For thepurposes of comparing matrices before and after restudy ofEuhelopus, we will track the type of changes to our respect-ive matrices, distinguishing changes between the ambiguousstate (“?”) and any unambiguous state (e.g. “0”, “1”) fromchanges between any two unambiguous states. Sereno (pers.comm., 2008) has called differences in the latter “characterstate conflict” and differences in the former “character stateresolution”, and has used them in a metric to quantify thedifferences between two matrices. The “Character State Sim-ilarity Index” (CSSI; P. Sereno, pers. comm., 2008) rangesbetween 0 (complete dissimilarity) and 1 (identity) and tal-lies the total number of character state conflicts (csc) andcharacter state resolutions (csr) relative to the total num-ber of character states (tcs) such that CSSI = (tcs – [csc +0.5csr])/tcs. In the special case in which a matrix is revised,as is the case here, it is useful to discriminate between twotypes of character state resolutions. That is, a scoring changefrom an unambiguous state (e.g. “0” or “1”) to an ambigu-ous state (i.e. “?”) is “adding ambiguity” whereas a scor-ing change from the ambiguous state to any unambiguousstate is “adding resolution”. “Adding ambiguity” increasesmissing data, while “adding resolution” reduces missingdata.

Twenty-two changes were made to the original Wilson(2002) matrix (NB: scoring adjustments made by Wilson[2005c] were not incorporated for the purposes of this reana-lysis). Of the 22 changes made, five were substantive changesbetween unambiguous states and have been noted in the de-scriptive part of the text. Of the remaining 17 changes, fourwere “adding resolution” and 13 were “adding ambiguity”.Many of the latter represent a more conservative scoring,rather than a loss of information from the skeleton of Eu-helopus. For instance, character 222 coded the size of theproximal condyle of metatarsals I and V proximal condylerelative to the inner metatarsals. Wilson (2002) scored thischaracter as derived on the basis of the size of metatarsal I re-lative to II–IV, but metatarsal V is not preserved. Despite thelikelihood that Euhelopus possessed the derived condition,this character was rescored to be unknown (“?”). Compar-ison of the Wilson (2002) matrix before and after restudyof Euhelopus indicates a CSSI of 0.9423. Reanalysis of therevised matrix yielded the same topology as Wilson 2002,in which Euhelopus positioned as the sister group of Titano-sauria. However, due to changes in characters 81 and 104,support for the node linking this clade dropped from a decayindex of 5 to 3.

Revision of the scorings of the Upchurch et al. 2004amatrix resulted in 81 changes. Of these changes, the majority


Table 5 Scoring changes for the character–taxon matrices of Wilson (2002) and Upchurch et al. (2004a), based on the redescriptionof Euhelopus zdanskyi presented here.

Analysis Scoring Changes

Wilson (2002) 1(1→0); 4(0→1); 25(?→0); 32(1→?); 34(0→1; 35(0→?); 39(? →1); 41(1→?); 42(1→?); 59(1→?); 66(?→1);74(0→?); 81(1→0); 100(?→0); 104(1→0); 187(0→?); 188(1→?); 191(0→?); 192(1→?); 222(1→?);229(1→?); 232(1→?)

Upchurch et al. (2004a) 5(0→?); 8(0→1); 11(0→1); 20(0→1); 23(1→?); 38(?→1); 39(?→0); 41(0→?); 62–64(0→?); 70(0→?);78(0→1); 90(0→?); 92(0→1); 94(1→0); 107(0→1); 109(?→0); 113(?→0); 116(0→1); 126(?→0); 127(?→1);130(?→0); 131(0→1); 134(?→0); 135(1→0); 136(?→1); 138(?→1); 140(?→1); 143(?→1); 144–146(?→9);148(1→2); 150(1→0); 151(?→0); 153(?→1); 154(?→0); 157(?→1); 158(1→0); 159(?→1); 168(1→?);201(?→1); 206(0→1); 217(?→0); 218, 219(?→1); 220–222(?→0); 242, 243(1→?); 244(0→?); 245(0→1);249(?→1); 251(1→?); 253, 254(?→1); 256(?→1); 261–264(?→1); 266, 267(?→1); 268(?→0);269–273(?→1); 274(1→0); 277(1→0); 279(?→1); 281(?→0); 288(?→0); 289(?→1); 306, 307(1→?)

See Table 6 for complete scorings. Wilson (2002) original versus rescored Character State Similarity Index (CSSI) = 0.9423; Upchurch et al. (2004a) originalversus rescored CSSI = 0.8414.

(49) added resolution, reducing total missing data. Fifteenscorings added ambiguity, which increased missing data butrepresent more conservative scoring. Seventeen changes in-volved the replacement of one known state by another. TheCSSI for Upchurch et al. (2004a) original versus rescoredis 0.8414. The differences in CSSI reflect the sources ofinformation on Euhelopus morphology available to Wilson(2002) and Upchurch et al. (2004a). Whereas Wilson (2002)used a combination of the published literature and directpersonal observation of the Euhelopus material, Upchurchet al. (2004a) relied solely on the published descriptions. Al-though monographic descriptions can provide a very usefuland generally accurate source of character data, direct ob-servation of the relevant specimens always provides a fullerunderstanding of anatomy and can offer unique insights intophylogenetic relationships.

The revised Upchurch et al. (2004a) data matrix wasanalysed using PAUP 4.0 (Swofford 2002) with the char-acter coding assumptions specified in the original ana-lysis. This produced over 200,000 most parsimonious trees(MPTs) (treelength = 654 steps) before the limit on com-puter memory meant that the analysis had to be halted. Thedata matrix was then analysed using the parsimony ratchetprogramme PAUPMacRat (Sikes & Lewis 2001) in order todetermine whether the original heuristic search had become

trapped in a “local” rather than “global” island of maximumparsimony. The shortest PAUPMacRat trees were also 654steps long, indicating that the original heuristic search hadprobably discovered a global maximum parsimony island. Asexpected, the substantial reduction in missing data (–11%),allowed more opportunity for character conflict and, as aconsequence, treelength increased 7 steps and tree numberincreased from 1,056 to more than 200,000.

In order to clarify the phylogenetic relationships of Eu-helopus, it was necessary to reduce the number of MPTs.Safe taxonomic reduction (Wilkinson 1995) was attempted,but all ingroup taxa have unique combinations of characterstates and no “safe” a priori deletions of taxa were identified.However, analyses of the original Upchurch et al. (2004a)data matrix indicated that three taxa (i.e. Lapparentosaurus,Nigersaurus and “Pleurocoelus-tex”) can be deleted withoutaffecting the relationships of the remaining ingroup taxa.There is no guarantee that this is also the case for the datamatrix that contains the revised Euhelopus scorings. Nev-ertheless, a priori deletion of these three genera is justifiedhere as a pragmatic step because the focus of the currentpaper is clarification of the relationships of Euhelopus, not aglobal reconstruction of sauropod relationships. Reanalysisof the revised data matrix after a priori pruning of Lap-parentosaurus, Nigersaurus and “Pleurocoelus-tex” yielded

Table 6 Revised scorings of Euhelopus zdanskyi for the matrices of Wilson (2002) and Upchurch et al. (2004a), based onthe redescription presented here

Analysis Scoring

Wilson 2002 01 1 1 0? 1 1 ? ? 1 ? ? ? ? 1 0? ? ? ? ? ? ? 0? ? ? ? ? ? ? 1 1 ? ? ? 01 1 ? ? ? ? ? ? ? ? ? ? ? ? ? ? 1 001 ? ?? ? ? ? 1 1 1 01 1 1 21 ? 1 01 1 ? 4 01 1 1 01 1 01 1 21 01 01 1 1 1 0 1 1 001 ? 03? ? 01 ? ? ? ? ? ? ? ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 1 0 1 1 ? ? ? ? ? ? 1 1 001 0000? 1 1 01 01 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?? ? ? 1 1 1 ? ? 01 ? ? 01 1 1 1 1 1 1 001 1 01 ? 1 01 1 1 ? 00? 1 1 1 0 1 ? 1 1 ? 1 ? 1 ? 1 1 ? ? 0

Upchurch et al. 2004a 1 1 00? 001 1 1 1 00001 1 01 1 1 0? ? 1 001 1 ? ? ? 1 ? 1 01 1 0? ? ? ? 0? ? ? ? ? ? ? ? ? ? ? ? 1 1 0?1 ? ? ? ? 1 1 01 ? 0? ? ? ? 1 1 1 1 1 1 1 1 1 1 1 000? 1 1 1 001 1 1 1 1 ? 1 1 1 1 1 1 1 00 1 1 001 1 021 01 000001 1 00 1 1 1 001 1 1 01 ? 1 1 0001 21 0 001 001 1 01 1 1 1 1 1 ? 00? ? ? ? ? ? ? ? ? ? ? ? ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 1 1 ? 1 ? ? 1 1 1 ? ? ? ? ? ? ? ? 01 1 0 00? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?? ? ? ? 1 ? 1 1 1 0 ? 1 1 1 01 01 01 1 1 1 1 1 1 1 01 1 1 1 1 01 1 01 1 1 01 ? 1 1 1 ? 01 1 1 1 001 ? 1 ? ? ?? 1 ? 1 ? ? ? 1 1

See Table 5 for scoring changes.


Figure 27 A strict consensus tree of the 97 topologies produced by the a posteriori deletion of Lourinhasaurus and Tehuelchesaurus from9,894 most parsimonious trees (MPTs) resulting from analysis of the revised Upchurch et al. (2004a) data matrix (see the text for details). KeyChinese taxa are in bold, and some terminal taxa have been combined into suprageneric taxa. Clade names assigned to major sauropod groupsare given. The asterisk next to Diplodocoidea indicates that Nemegtosaurus and Quaesitosaurus were included within this clade by Upchurchet al. (2004a).

9,894 MPTs (treelength = 634). The parsimony ratchet wasapplied once again and the results suggest that the heuristicsearch found the shortest trees globally.

A strict consensus tree of the 9,894 MPTs indicatesthat Euhelopus and Phuwiangosaurus are basal somphos-pondylan sauropods that lie just outside of Titanosauria (seeWilson & Upchurch 2003 for clade name definitions). Theserelationships are shown in Fig. 27, which is a reduced con-sensus cladogram (Wilkinson 1994) based on the 291 topo-logies remaining after the a posteriori deletion of Lourin-hasaurus and Tehuelchesaurus from the 9,894 MPTs.

The support for the position of Euhelopus was examinedusing bootstrap analysis, decay analysis and constrained to-pologies. Bootstrap analyses were conducted using 10,000replicates and the heuristic search in PAUP 4.0. The boot-strap support for the node uniting Euhelopus with Titano-sauria is 55%. The decay index of this node is 1. Despite thislow value, support at other nodes (i.e. Titanosauriformes,Macronaria) robustly nest Euhelopus within Neosauropoda.A constraint was written in order to force Euhelopus to lieoutside Neosauropoda – the position favoured by Upchurchet al. (2004a; Fig. 4). An heuristic search of the data matrix(with the Euhelopus rescorings and the a priori exclusionof Lapparentosaurus, Nigersaurus and “Pleurocoelus-tex”)produced 34 MPTs of length 645, which is 11 steps longerthan the most parsimonious solution. A Templeton test com-pared these constrained MPTs with those produced withouta constraint, yielding p-values of 0.056–0.14, just outside the95% confidence window. (NB: the strict reduced consensustree [Fig. 27] positions Jobaria outside Neosauropoda, a res-

ult that is in accord with Wilson [2002] but differs fromUpchurch et al. [2004a], which identified Jobaria as a basalmacronarian. Simply by revising the scorings for Euhelopus,the Upchurch et al. data produces topologies that are moresimilar to those found by Wilson [2002], not only in terms ofthe position of Euhelopus but also for Jobaria as well, eventhough the scorings for the latter remain unchanged.)

The results of these tests indicate that the placement ofEuhelopus within basal Somphospondyli is only moderatelysupported. In the case of the bootstrap and decay analyses,it is not clear whether: (1) the position of Euhelopus is un-stable; or (2) its position is actually well supported but thebootstrap and decay values are low because other taxa (e.g.Phuwiangosaurus, Austrosaurus) change their relationshipsrelative to Euhelopus with little cost in terms of tree length.The constrained analyses indicate that 11 additional steps arerequired to force Euhelopus into a position outside Neosaur-opoda. Although there is a sizable parsimony penalty associ-ated with this topological rearrangement, the Templeton testdemonstrates that it cannot be statistically excluded (with95% confidence) as an explanation of the data.

Euhelopus and the biogeographical historyof East Asian sauropods

Euhelopus has played an important role in two recent debatesconcerning the biogeographical history of East Asian sauro-pods: (1) the existence of a monophyletic Euhelopodidae hasbeen linked to the geographical isolation of East Asia fromthe Middle Jurassic to the Early Cretaceous (Upchurch 1995,


1998); and (2) the placement of Euhelopus at the base of theTitanosauria potentially reinforces recent suggestions thatthis group originated in Laurasia in general (Weishampel &Jianu 1997) or East Asia in particular (You et al. 2003). Aquantitative biogeographical analysis of sauropods, based ontheir phylogenetic relationships, lies outside the scope of thecurrent study. Nevertheless, resolution of the phylogeneticrelationships of Euhelopus presents an opportunity to revisitthese debates and address some of the problems that mayhinder future progress.

East Asian isolationThe distinctive nature of Middle Jurassic to Early CretaceousChinese terrestrial faunas (including dinosaurs, pterosaursand mammals) has led several authors to suggest thatendemism occurred as a result of geographical isolation(Milner & Norman 1984; Dong 1992; Russell 1993, 1995;Russell & Zheng 1993; Upchurch 1995; Luo 1999; Barrettet al. 2002). There are at least two geographical barriers thatcould have isolated East Asia from the rest of Pangaea duringthe Middle Jurassic: (1) the Turgai (= “Obik” and “Uralian”)epicontinental sea between Europe and central Asia (Milner& Norman 1984; Russell 1993, 1995; Smith et al. 1994;Upchurch 1995; Le Leouff 1997; Upchurch et al. 2002;Scotese 2004; Blakey 2006); and (2) the Mongol-Okhotsksea between Siberia–Kazakhstan and the Mongolian–Tarim–Junggar blocks (Enkin et al. 1992; Upchurch 1995; Barrettet al. 2002), which closed in the Late Jurassic or Early Creta-ceous (Cogne et al. 2005). Most authors believe that the endof the isolation of East Asia occurred in the Early Cretaceousas a result of the establishment of dispersal routes withEurope and/or North America (Weishampel & Bjork 1989;Le Loeuff 1991, 1997; Russell 1993, 1995; Currie 1995;Manabe & Hasegawa 1995; Upchurch 1995; Buffetaut et al.1997; Norman 1998; Buffetaut & Suteethorn 1999; Barrettet al. 2002; Canudo et al. 2002; Holtz et al. 2004). The pre-ferred date of the end of isolation varies from Late Jurassic toEarly Tertiary and depends partly on which of the potentialpalaeogeographical barriers is favoured and partly on whichtaxonomic groups are considered (Milner & Norman 1984;Weishampel & Bjork 1989; Russell 1993; Manabe &Hasegawa 1995; Upchurch 1995; Le Loeuff 1997; Barrettet al. 2002; Upchurch et al. 2002). For example, Russell(1993) and Upchurch et al. (2002) argued that isolationended during the Aptian–Albian, when marine regressioncaused the Turgai Sea to retreat and allowed iguanodontiandinosaurs and paramacellotid lizards to invade East Asiafrom Europe. It is also possible that a land connectionacross the Bering Strait formed at approximately the sametime, enabling dispersals between East Asia and westernNorth America (Weishampel & Bjork 1989). Barrett etal. (2002), however, noted the presence of titanosauriformsauropods in East Asia in rocks as old as the Valanginianand, therefore, proposed that isolation ended earlier thanpreviously suspected. Although Barrett et al. (2002) did notspecify the palaeogeographical mechanism responsible forthis earlier end to isolation, their scenario is more compatiblewith the closure of the Mongol–Okhotsk sea than it is withthe Aptian–Albian marine regression.

Sauropods have played an important role in the EastAsian isolation hypothesis (EAIH). Russell (1993) proposedthat “mamenchisaurs” were restricted to East Asia, whereas

diplodocids were absent from this area but endemic to the restof Pangaea. This view received support from the cladogramspresented by Upchurch (1995, 1998), in which the Middleand Late Jurassic Chinese taxa Shunosaurus, Omeisaurus,Mamenchisaurus and Euhelopus (now thought to be EarlyCretaceous in age) formed a monophyletic group of basaleusauropods termed the Euhelopodidae, whereas neosauro-pod lineages were apparently restricted to the rest of Pangaeaduring this portion of the Mesozoic. Wilson & Sereno (1998)cast doubt on the monophyly of the Euhelopodidae and sug-gested that neosauropod lineages had become widespreadacross Pangaea (including East Asia) prior to the Middle Jur-assic and that regional faunal differences were largely causedby differential survival. Furthermore, Rich et al. (1999) notedthe morphological similarity of Tehuelchesaurus (from SouthAmerica) to Omeisaurus, and therefore argued that faunalinterchange between East Asia and the rest of Pangaea waspossible during the Middle Jurassic (NB: Tehuelchesaurusis now known to have been collected from the CanadonCalcareo Formation, which is Late Jurassic in age, muchyounger than the Middle Jurassic Canadon Asfalto Form-ation: Rauhut 2003, 2006). Barrett et al. (2002) reviewedmuch of the previous literature and identified two compet-ing biogeographical hypotheses to explain the presence oftitanosauriform sauropods in the earliest Cretaceous of EastAsia: either (1) these taxa invaded East Asia at this timeas a result of the end of isolation; or (2) neosauropod lin-eages were present in East Asia since the Middle Jurassicand their “sudden” appearance in the Early Cretaceous is anartefact of a patchy sampling of the fossil record. Barrettet al. (2002) preferred the first explanation (i.e. EAIH) partlybecause of the absence of neosauropods in the Jurassic ofEast Asia and, partly, because the cladogram presented byUpchurch (1998), in which euhelopodids are monophyletic,was the best-supported and most detailed sauropod phylo-geny available to them at that time. Thus, the isolation ofEast Asia from the Middle Jurassic onwards could explainthe evolution of the endemic euhelopodid clade, and the endof isolation in the Early Cretaceous might also account forthe disappearance of this group and their replacement by ti-tanosauriforms and perhaps other neosauropods (Upchurch1995, 1998).

Since Barrett et al.’s (2002) study, however, new phylo-genetic analyses have shifted the balance of evidence so thathypothesis (2), above, may be better supported. Firstly, it ispossible that at least one neosauropod lineage was presentin East Asia during the Middle Jurassic: Bellusaurus fromwestern China was tentatively identified as a titanosaur byJacobs et al. (1993), and the cladistic analysis of Upchurchet al. (2004a) placed it as a basal macronarian. However, re-jection of the EAIH (i.e. Barrett et al. hypothesis “1”), basedon Bellusaurus alone, should be treated with caution: reana-lysis of the Upchurch et al. 2004a data matrix presented hereresults in Bellusaurus being placed outside the Neosauro-poda. Secondly, most recent sauropod phylogenies (includ-ing the reanalyses here) agree that the Euhelopodidae (sensuUpchurch 1995, 1998) represents a polyphyletic assemblage(Wilson & Sereno 1998; Wilson 2002; Upchurch et al. 2004a;Curry Rogers 2005; Harris 2006), although whether Euhel-opus itself should be placed inside or outside of the Neosaur-opoda has remained controversial until the current study.

The breakdown of euhelopodid monophyly has beenregarded as undermining the EAIH (Wilson & Sereno 1998;


Barrett et al. 2002). It could be argued that Barrett et al.’s(2002) hypothesis (2) should be preferred and the conceptof East Asian isolation (at least as an explanation for saur-opod biogeographical distributions) should be abandoned.Such a conclusion, however, would be premature because itis possible to reconcile the new interpretations of the relation-ships of East Asian sauropods with the EAIH. In particular,Wilson (2005a) has noted that all pre-Cretaceous Asian saur-opods are non-neosauropods, whereas all Cretaceous Asiansauropods are members of Somphospondyli. Thus, the para-phyletic or polyphyletic assemblage of “euhelopodid” saur-opods could represent a relictual fauna that existed in EastAsia during the Jurassic, being replaced by more advancedneosauropod lineages that dispersed to this area during theEarly Cretaceous. This scenario enables continued supportfor the EAIH even though the monophyly of the Euhelopo-didae (sensu Upchurch 1995) has broken down. Finally, theexpectation that East Asian isolation should have resulted inthe evolution of a multi-species endemic clade is problem-atic. Vicariance can be manifested at a variety of taxonomicscales, depending on the amount of time elapsed and therates of evolutionary change in different lineages. Indeed,the evidence for vicariance can actually be strengthened byre-arrangements of the phylogenetic relationships of taxathat disrupt the monophyly of endemic clades. In order toexplain this point more fully, a brief aside concerning areacladograms and vicariance is required (see below).

Vicariance and area cladogramsThe emergence of a geographical barrier can divide a singlespecies into two isolated populations that eventually divergeto become two daughter species via allopatric speciation. Oneor both of these daughter species can then radiate within thatendemic area to produce an endemic clade. Euhelopodidaehas been proposed as one such endemic clade created by thegeographical isolation of East Asia. However, phylogeneticbiogeographers (e.g. Brooks & McLennan 2002) have arguedthat the existence of an endemic clade, by itself, providesonly relatively weak evidence for vicariance because onlythe basal node represents a vicariant event (i.e. the separa-tion of the endemic lineage from its sister taxon outside theregion of endemism). All other nodes within the endemicclade have resulted from either allopatric speciation withinthe area of endemism or sympatric speciation. Fortunately,the emplacement of a geographical barrier has the poten-tial to isolate many different species and create multipleendemic clades. Although differences in dispersal capabil-ity and evolutionary rate may affect response to the imposedbarrier (Simpson 1952), geographical isolation can be expec-ted to affect multiple species. Thus, evidence for vicarianceis strengthened when congruent spatiotemporal patterns arefound in multiple, independent lineages (Nelson & Platnick1981; Lieberman 2000; Hunn & Upchurch 2001; Brooks &McLennan 2002).

Perhaps counterintuitively, stronger evidence for vicari-ance can arise when a supposed endemic clade (e.g. Euhel-opodidae) is disbanded, and its constituent taxa are redis-tributed among other clades. This point is illustrated by ahypothetical example. In Figure 28A, the 16 taxa (1–16)form four monophyletic clades (W–Z), each of which is en-demic to one of the four geographical areas (A–D). Sucha pattern is consistent with a geographical history in which

Figure 28 Two hypothetical scenarios depicting the phylogeneticrelationships and biogeographical ranges of taxa 1–16. A–D representfour separate geographical areas that were once in contact and thenbecame isolated from each other in the sequence (A, (B, (C, D))). Theseparation of A from BCD is event 1 (e1); B from CD is event 2 (e2); andC from D is event 3 (e3). (A) shows the 16 taxa in four monophyleticgroups, such that each clade (W–Z) is found in only one of the fourareas. (B) Shows the same taxa in a different set of relationships sothat, despite the disruption of clades W–Z, there is still evidence forvicariance in the form of the number of nodes consistent with one ofthe geographical events.

the once continuous area ABCD fragmented in the sequence(A (B (C D))). However, the confinement of each clade toa single area means that the support for vicariance is weakbecause there is only one cladogenetic event associated witheach geographical isolation event (Fig. 28A). Now considerthe phylogenetic pattern in Figure 28B, in which the relation-ships of the 16 taxa have been altered so that the monophylyof the clades W–Z has been disrupted. Despite the break-down of monophyly with respect to each area, the evidencefor vicariance has actually become much stronger, becauseeach of the geographical isolation events is supported byfour cladogenetic events in the phylogeny (Fig. 28B). Forexample, each of the four clades independently supports thehypothesis that the first vicariance event involved the separ-ation of area A from area BCD (event “e1” in Fig. 28B).

The hypothetical example outlined above demonstratesthat the monophyly of Euhelopodidae can break downwithout weakening the evidence for vicariance caused byEast Asian isolation: indeed, the evidence for vicariancecould actually become stronger. Whether the breakdown ofEuhelopodidae has weakened or strengthened support for theputative vicariance event cannot be judged merely from qual-itative inspections of the alternative phylogenetic positions


of taxa such as Shunosaurus, Omeisaurus, Mamenchisaurusand Euhelopus proposed by Wilson (2002), Upchurch et al.(2004) and the current study. This is because vicariancepatterns are easily obscured by missing data and coherentdispersal events that make it difficult to identify congru-ence among area relationships (Lieberman 2000; Upchurch& Hunn 2002; Halas et al. 2005). Therefore, the impactof new phylogenetic topologies on the evidence for vicari-ance should be assessed using biogeographic methods thatidentify and test congruent area relationships in large andcomplex data sets and evaluate the probability of obtain-ing such patterns by chance (Page 1991; Lieberman 2000;Brooks & McLennan 2002; Upchurch & Hunn 2002; Halaset al. 2005). Such an analysis of dinosaurian, or even sauro-pod, biogeography lies outside the scope of the current study.Consequently, we simply note at this time that the effects ofour revision of Euhelopus as a basal somphospondylan on theEAIH will remain unknown until quantitative biogeograph-ical methods are applied in the future.

The biogeographical origin of titanosaursHistorically, the first discoveries of titanosaur material weremade in the southern hemisphere (Wilson & Upchurch 2003).Consequently, many authors suggested that titanosaurs rep-resent a group that originated in Gondwana after it be-came isolated from Laurasia in the Jurassic or Early Creta-ceous (von Huene 1932; Bonaparte 1984, 1999; Bonaparte& Kielan-Jaworowska 1987; Lucas & Hunt 1989; Astibia etal. 1990; Jacobs et al. 1993; Russell 1993; Le Loeuff & Buf-fetaut 1995; Upchurch 1995; Le Loeuff 1997). Note that thisconcept originated within the fixist view of continental con-figuration but was easily adapted to the modern plate tectonicparadigm. Despite the subsequent discovery of titanosaurs inLaurasia (e.g. “Titanosaurus” in Europe and Alamosaurus inNorth America), this group still seemed to be most abund-ant and diverse in Gondwana. Thus, titanosaurs have be-come an iconic example of a Gondwanan radiation and theirappearance in Laurasia is usually explained via northwarddispersal (e.g. Lucas & Hunt 1989; Le Loeuff & Buffetaut1995).

In recent years, however, the Gondwanan origin of ti-tanosaurs has been challenged on the basis of several linesof evidence. An influx of new discoveries and the results ofphylogenetic analyses have identified many northern hemi-sphere titanosaurs, including some particularly early forms.For example, Day et al. (2002, 2004) described some ofthe earliest evidence for titanosaurs – wide-gauge track-ways from Bathonian age deposits from Ardley (Oxford-shire, England). Furthermore, taxa such as Venenosaurusfrom North America, “Pelorosaurus becklesii” from Europeand Phuwiangosaurus from Asia, suggest that titanosaurs (orat least basal somphospondylans) were widespread acrossLaurasia during the Early Cretaceous (Upchurch 1995;Tidwell et al. 2001; Wilson & Upchurch 2003; Upchurchet al. 2004a; Wilson 2005).

The reaction to these advances has been varied. Someauthors have proposed that titanosaurs originated in Laurasia(Weishampel & Jianu 1997) or in Asia (You et al. 2003).An alternative to these “Laurasian origin” hypotheses is theview that titanosaurs evolved during the Early Jurassic orearly Middle Jurassic and dispersed across Pangaea prior tothe major fragmentation events in the Late Jurassic and Early

Cretaceous (Wilson & Sereno 1998; Day et al. 2002, 2004;Upchurch et al. 2002; Wilson & Upchurch 2003; Canudo &Royo-Torres 2004; Upchurch & Barrett 2005). In this scen-ario, the origin of Somphospondyli and Titanosauria can-not be traced to vicariance events (at least at the scale ofcontinental fragmentation), although vicariance at a lowertaxonomic level (e.g. the genus) could occur. Proponents ofthis early and global radiation disagree about the impact ofPangaean fragmentation on dinosaur evolution and distribu-tion during the Late Jurassic and Cretaceous. Some workers(e.g. Wilson & Sereno 1998; Sereno 1999) have suggestedthat subsequent differences in the composition of dinosaurfaunas were the result of regional extinctions operating on aonce cosmopolitan assemblage. Others, however, have iden-tified vicariance patterns among Cretaceous titanosauriangenera that correspond to the break-up sequence for Pangaea(Upchurch et al. 2002; Canudo & Royo-Torres 2004).

In our view, several factors shift the balance of evidencein favour of the biogeographical hypothesis that titanosaursappeared relatively early (i.e. in or before the Middle Jur-assic) and acquired a virtually global distribution prior toPangaean fragmentation.

(1) Although the occurrence of many basal titanosaurs (orbasal somphospondylans) in the Early Cretaceous of EastAsia is intriguing, there are dangers in extrapolatingbiogeographical inferences directly from this observa-tion. As was shown above, basal phylogenetic positionsof taxa in area A can be caused by vicariance in whicharea A is separated from the rest of the world first. Thismeans that area A (the most basal area in the area clado-gram) could either be the “centre of origin” for a clade,or it might simply be the first area to have become isol-ated after the clade became widespread across ABCD(Croizat et al. 1974). Which scenario we prefer dependson whether the area cladogram for the clade of interestis congruent with a more general pattern indicative ofvicariance, which in turn determines the parsimony pen-alties associated with the competing “vicariance” and“centre of origin + dispersal” interpretations (Brooks &McLennan 2002). In the absence of a quantitative phylo-genetic biogeographical analysis, the simple observationthat basal members of a clade occupy a particular areashould not be used to favour a centre of origin hypothesisover vicariance, or vice versa.

(2) It seems probable that titanosaurs had a global distribu-tion in the Early Cretaceous. However, the Early Creta-ceous dinosaur fossil record of East Asia (i.e. China) isparticularly rich compared to that in Europe and NorthAmerica. It is, therefore, possible that the accumulationof East Asian forms at the base of the clade is an artefactcreated by unequal sampling of the fossil record or oftaxon selection by phylogeneticists who have favouredmore complete specimens. This possibility can be testedby future phylogenetic analyses by targeting the inclu-sion of Early Cretaceous titanosaurs from outside EastAsia.

(3) The presence of statistically robust area cladograms(Upchurch et al. 2002), divergence time estimates(Upchurch & Barrett 2005) and direct observations oftrackway data (Wilson & Carrano 1999; Day et al. 2002,2004) all suggest that somphospondylans and perhaps amore derived titanosaur clade had diverged from other


sauropod lineages by the Bathonian at the latest. Thus,the basal taxa cited by You et al. (2003) occured 20–40million years after the true origin of the clade and may,therefore, not provide a sound guide to its “centre oforigin”.

In short, the patchy sampling of the titanosaur fossilrecord (especially during the Middle and Late Jurassic), un-certainty of ages of several key deposits and lack of resolu-tion for basal titanosaur interrelationships mean that recon-structions of the timing and place of origin of titanosaursshould be treated with great caution. Nevertheless, currentevidence clearly demonstrates that the titanosaurian lineagehad diverged from other sauropods by the Bathonian; con-sequently, proposals that titanosaurs originated in either EastAsia or Gondwana are inconsistent with our best estimatesof their spatiotemporal distribution.

Resurrecting Euhelopodidae?Canudo et al. (2002) described teeth from the Barremian ofSpain that possess bosses on the lingual part of each crown.Such lingual crown buttresses are also present in Euhelopus(see above) and have been recognised as an autapomorphyof the genus (Wilson & Sereno 1998: 22). More recently,Buffetaut et al. (2002) and Barrett & Wang (2007) describedisolated teeth from the Early Cretaceous of Thailand andChina, respectively, several of which also possess these lin-gual crown buttresses. Finally, Ksepka & Norell (2006) de-scribed a partial skeleton of the titanosauriform Erketu fromthe Early Cretaceous of Mongolia. This material does not in-clude teeth, but the cervical vertebrae of Erketu share a num-ber of derived states with Euhelopus such as extreme elong-ation of the centrum, “pre-epipophyses” and prong-like epi-pophyses (see above). The phylogenetic analysis of Ksepka& Norell (2006) placed Erketu within basal Somphospondyliin a trichotomy with Euhelopus and Titanosauria, but theydid not take into account the characters mentioned above thatcould uniquely unite these two East Asian genera.

We agree with Canudo et al. (2002) that there may exista hitherto unsuspected clade of basal titanosauriforms thatwas widespread across Asia and possibly Europe during theEarly Cretaceous (Table 7). In the future, it may be use-ful to resurrect the term Euhelopodidae as the name for theclade of titanosauriforms closely related to Euhelopus, butwe strongly recommend foregoing formalization of this orany other clade name in the absence of a detailed phylogen-etic analysis corroborating monophyly of the group and therobustness of the results. In addition, there are a number ofnewly discovered Asian titanosauriforms (see Table 7) await-ing fuller description that would be critical for inclusion inany phylogenetic assessment of basal titanosauriforms.

Conclusion

Continued interest in dinosaur systematics, combined withthe mechanistic ease of cladistic methodology (Grant et al.2003) and an ever-growing store of character datasets, hasled to a dramatic increase in the number of hypotheses for di-nosaur interrelationships since the first major analyses werepublished more than 20 years ago (Gauthier 1986; Sereno1986). More than a score of cladistic analyses have fo-cused on Sauropodomorpha and its subgroups alone (e.g. see

Barrett & Batten 2007). This proliferation of analyses hasled to many competing hypotheses of interrelationships thatconflict, sometimes substantially, with one another – evenwithin the body of work of one author.

Transparency is central to cladistic methodology andthis attribute allows authors to evaluate previous research-ers’ characters and character states, coding strategy, scoring,search methodology and consensus techniques. Critical eval-uation of these data is part of the research cycle (Kluge 1991;Jenner 2001), but reassessment of previous work is seldomperformed, which can lead to long-standing disagreementsabout interrelationships of important groups. One potentialexplanation for this lack of comparative critique may bethat there is no methodology for comparisons of compet-ing datasets, although some researchers (e.g. Sereno 2007,pers. comm., 2008) have taken steps in this direction.

The phylogenetic affinities of Euhelopus and otherChinese taxa have been the focal disagreement among sauro-pod systematists for a decade, despite exchanges in the liter-ature (Upchurch 1995, 1998; Wilson & Sereno 1998; Wilson2002; Upchurch et al. 2002, 2004a). Although this type ofexchange is a valuable exercise, it can be time-consumingand allows debates to continue because authors misunder-stand each other or get bogged down in semantic debates. Analternative approach, in which disagreeing systematists worktogether, is rare (e.g. Rieppel & Reisz 1999) but has severaladvantages. Poorly defined characters and character statescan be identified and redefinitions can be found. Characterscorings can be discussed and agreed upon, or, if ambiguityremains, agreement to score a state as “?” can be made. Issuesregarding the association, articulation and referral of speci-mens can be jointly reevaluated – enabling more uniformscorings. Finally, more accurate and wide-ranging comparis-ons between the focal taxa and other forms can be achieved,because workers can combine their knowledge of specimensthat perhaps only one of them has examined.

The revised Wilson (2002) and Upchurch et al. (2004a)data matrices both support the view that Euhelopus is thesister taxon to Titanosauria. Derived states supporting thisposition include: single pre- and postspinal laminae on dorsalneural spines; six co-ossified sacral vertebrae; medial deflec-tion of scapular glenoid; medial deflection of proximal partof the femur; and camellate bone tissue structure in presacralvertebrae.

Our conclusion that Euhelopus is a basal somphospon-dylan further disrupts the monophyly of the “Euhelopodidae”and indicates that East Asian sauropods, from the MiddleJurassic to Early Cretaceous, comprised several disparatelineages rather than a single endemic clade. Nevertheless, aperiod of isolation of East Asia, during the Middle and LateJurassic, is still feasible. Although there still exists the pos-sibility that Euhelopus or Euhelopus-like taxa were present(but currently unrecorded) in Jurassic sediments in East Asiaduring its period of geographical isolation, we consider itmore likely that Euhelopus was an Early Cretaceous immig-rant to East Asia. Although the basal position of Euhelopuswith respect to other titanosaurs further undermines previ-ous claims that this clade originated in Gondwana, it wouldbe premature to conclude that the balance of evidence hasshifted to a Laurasian or even East Asian centre of origin.The relationships of many other basal titanosaurs and ti-tanosauriforms must be clarified before the impact of EastAsian isolation and the break up of Pangaea on sauropod


Table 7 Cretaceous Asian sauropod species, listed in order of their stratigraphic appearance.

Taxon Formation Country Age Reference Material

Nemegtosaurusmongoliensis (T)

Nemegt Mongolia Maastrichtian Nowinski 1971 Skull

Opisthocoelicaudiaskarzynskii (T)

Nemegt Mongolia Maastrichtian Borsuk-Bialynicka1977

Postcranial skeleton lackingneck

‘Nemegtosaurus pachi’ (n.d.) Subashi China ?Campanian–Maastrichtian

Dong 1977 Tooth

Quaesitosaurus orientalis (T) Barungoyot Mongolia Santonian–Campanian

Kurzanov & Bannikov1983

Skull

Sonidosaurussaihangaobiensis (T)

Erlian China Senonian Xu et al. 2006 Partial skeleton

unnamed (?TSF) Kasamatsu Japan Santonian Tanimoto & Suzuki1998

Teeth

‘Antarctosaurus’ jaxarticus’(n.d.)

DabrazinskayaSvita

Kazakhstan Turonian–Santonian

Ryabinin 1939 ?

Unnamed ‘diplodocoid’ Dzarakuduk Uzbekistan Turonian Sues & Averianov 2004 Teeth, postcranial bonesHuabeisaurus allocotus (?T) Huiquanpu China Late Cretaceous Pang & Cheng 2000 2 teeth, nearly complete

postcraniumQingxiusaurus youjiangensis

(?T)“Redbeds” China Late Cretaceous Mo et al. 2008 Anterior caudal neural spine,

sternal plate, humerusBorealosaurus wimani (T) Sunjiawan China Early Late

CretaceousYou et al. 2004 Caudal vertebra

Dongyangosaurus sinensis(T)

Fangyan China Early LateCretaceous

Lu et al. 2008 10 dorsal vertebrae, sacrum,first 2 caudal vertebrae,dorsal ribs, ilia, pubis,ischium

Gobititan shenzhouensis(TSF)

Xinminbao Group China Albian You et al. 2003 Caudal vertebrae, distalhindlimb

unnamed Jiufotang China Albian Wang et al. 1998 ?Tangvayosaurus hoffeti (TSF) Gres Superieurs Laos Aptian–Albian Allain et al. 1999 Partial skeletonJianshanosaurus lixianensis

(?T)Jinhua China Aptian–Albian Tang et al. 2001b 5 dorsal and 3 caudal

vertebrae, partial scapula,pubis, ischium and femur

Shestakovo sauropod (TSF) Ilek Russia Aptian–Albian Averianov et al. 2002 Teeth, mid-caudal vertebrae,pes

‘Ultrasaurus tabriensis’ (n.d.) Gugyedong South Korea Aptian Kim 1983; Lee et al.1997

Partial humerus

Chiayusaurus lacustris (?TSF) Xinminbao Group China Barremian–Aptian Bohlin 1953 Toothunnamed (TSF) Xinminbao Group China Barremian–Aptian Dong 1997 Cervical vertebraunnamed ‘brachiosaurid’

(?TSF)Jinju South Korea Barremian–Aptian Lim et al. 2001 Tooth

Dongbeititan dongi (TSF) Yixian China Barremian Wang et al. 2007 Partial skeletonPukyongosaurus millenniumi

(TSF)Hasandong South Korea Barremian Dong et al. 2001 7 partial cervical vertebrae,

dorsal centrum, ribs,chevrons

‘Chiayusaurus asianensis’(n.d.)

Hasandong South Korea Barremian Lee et al. 1997, 2001 Tooth

unnamed ‘titanosaurid’(indet.)


unnamed ‘camarasaurid’(indet.)


Euhelopus zdanskyi (TSF) Mengyin China ?Neocomian Wiman 1929 2 partial skeletonsunnamed (TSF) Kuwajima Japan ?Barriasian–

?HauterivianBarrett et al. 2002 9 teeth

unnamed ‘brachiosaurid’(?TSF)

Kitadani Japan Hauterivian–Barremian

Azuma 2003 Teeth

Toba sauropod (?TSF) Matsuo Group Japan Valangian–Barremian

Tomida & Tsumura2006

2 partial caudal vertebrae,2 partial limb bones

‘Asiatosaurus mongoliensis’(n.d.)

Oshih Mongolia Early Cretaceous Osborn 1924b 2 teeth

Mongolosaurus haplodon(?T)

On Gong Mongolia Early Cretaceous Gilmore 1933 Tooth, basisphenoid, cervicalvertebrae 1–3

Erketu ellisoni (TSF) Bor Gove Mongolia Early Cretaceous Ksepka & Norell 2006 Anterior cervical series, sternalplate, distal hindlimb


Table 7 Continued

Taxon Formation Country Age Reference Material

Phuwiangosaurussirindhornae (T)

Sao Khua Thailand Early Cretaceous Martin et al. 1994 Multiple skeletons

Fusuisaurus zhaoi (TSF) Napai China Early Cretaceous Mo et al. 2006 Anterior caudal vertebrae, dorsalribs, ilium, pubis, distal femur

Huanghetitan luijiaxiaensis(TSF)

Hekou Group China Early Cretaceous You et al. 2006 Sacrum, 2 caudal vertebrae,fragmentary cervical ribs,partial chevron, scapula,coracoid

‘Asiatosaurus kwanshiensis’(n.d.)

Napan China Cretaceous Hou et al. 1975 Tooth, partial vertebra, ribs

Jiutaisaurus xidiensis (n.d.) Quantou China Cretaceous W.-H. Wu et al. 2006 18 anterior caudal vertebrae &chevrons

Youngest species are at the top and oldest species are at the bottom; Early and Late Cretaceous species are separated by solid line. Parenthetical abbreviationsafter species name indicate phylogenetic affinities: indet., indeterminate sauropod; n.d., nomen dubium; T, Titanosauria; TSF, Titanosauriformes.

evolutionary history can be fully assessed. We anticipatethat the relationships of Euhelopus relative to other basalsomphospondylans and titanosaurs will become more fullyresolved in the near future, when newly discovered taxa aredescribed in more detail and systematic effort is directedtowards the interrelationships of Titanosauriformes.

Acknowledgements

We thank S. Stuenes and J. Peel for access to the collec-tions of the PMU and for allowing us to publish archivalphotographs (Figs 5 & 26). We thank B. Miljour for draftingFigure 1 and for her assistance with the Supplementary Fig-ures. P. Barrett kindly provided information on microwearin isolated Euhelopus teeth, as well as other useful inform-ation. N. Insel translated the original description of Euhel-opus by Wiman (1929), which is available on the PolyglotPaleontologist website. We are grateful to P. Barrett, P. Man-nion and S. Upchurch for their help with data collectionand photos. S. Upchurch also provided insightful observa-tions on the “K” lamina. We thank P. Sereno for allowingus to use the Character State Similarity Index defined in hisin review manuscript. M. D’Emic, T. Ikejiri, P. Mannion,L. Salgado, J. Whitlock and an anonymous referee providedcareful reviews of the manuscript. J.A.W.’s research was sup-ported by National Science Foundation grant DEB-0640434and a Woodrow Wilson National Fellowship Foundation Ca-reer Enhancement Fellowship for Junior Faculty.

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