Cretaceous Research 27 (2006) 364e376www.elsevier.com/locate/CretRes

Ligabuesaurus leanzai gen. et sp. nov. (Dinosauria, Sauropoda), a newtitanosaur from the Lohan Cura Formation (Aptian, Lower Cretaceous)

of Neuquen, Patagonia, Argentina

Jose F. Bonaparte a,*, Bernardo J. Gonzalez Riga b, Sebastian Apesteguıa a

a Seccion de Paleontologıa de Vertebrados, Museo Argentino de Ciencias Naturales, Av. �Angel Gallardo 470, 1405 Buenos Aires, Argentinab Instituto Argentino de Nivologıa, Glaciologıa y Ciencias Ambientales, Centro Regional de Investigaciones Cientıficas y Tecnologicas,

Avda Ruiz Leal s/n Parque Gral. San Martın, 5500 Mendoza, Argentina

Received 3 November 2004; accepted in revised form 15 July 2005

Available online 9 May 2006

Abstract

Ligabuesaurus leanzai gen. et sp. nov. is a new titanosaur (Saurischia, Sauropoda) from the Lower Cretaceous of Neuquen Basin, north Pa-tagonia, Argentina. The fossil remains were found in the upper section of the Lohan Cura Formation, which is regarded as Late AptianeAlbianin age. Remains include an incomplete maxilla with ten teeth, six cervical and dorsal vertebrae, and several associated girdle and limb bones.Ligabuesaurus is characterized by: (1) laminar and anteroposteriorly compressed neural spines on posterior cervical and anterior dorsal vertebraethat are rhomboid in shape and wider than vertebral centra; (2) spinoprezygapophyseal laminae in the posterior cervical vertebrae forked to formtwo pairs: the medial laminae contact one another toward the tip of the neural spine, and the lateral pair form the lateral border of the neuralspine; (3) dorsoventrally reduced neural arch pedicels in posterior cervical and anterior dorsal vertebrae; and (4) rudimentary prespinal lamina onposterior cervical and anterior dorsal vertebrae. A preliminary phylogenetic analysis suggests that Ligabuesaurus is a basal titanosaur. The de-velopment of relatively long forelimbs, with a humerus/femur ratio of 0.9, indicates that this condition is not an exclusive adaptation of theBrachiosauridae.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Neuquen Basin; Patagonia; Sauropod; Early Cretaceous

1. Introduction

Cretaceous dinosaurs are particularly abundant in SouthAmerica. The diverse records assigned to Late Hauterivian(Salgado and Bonaparte, 1991), Aptian (Del Corro, 1975;Bonaparte, 1999b; Apesteguıa and Gimenez, 2001a,b), LateAlbian (Calvo and Bonaparte, 1991; Calvo and Salgado, 1995),Cenomanian (Bonaparte and Coria, 1993), Coniacian (Huene,1929; Gonzalez Riga, 2002, 2003; Calvo and Gonzalez Riga,2003; Powell, 2003), Santonian - Late Campanian (Arid andVizotto, 1971; Powell, 1987a,b; Salgado and Coria, 1993;

* Corresponding author. Present address: Instituto de Neurobiologıa,

Serrrano 669, 2nd floor, 1414 Buenos Aires, Argentina.

E-mail address: bonajf@fibertel.com.ar (J.F. Bonaparte).

0195-6671/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.cretres.2005.07.004

Salgado, 1996; Salgado et al., 1997b; Campos and Kellner,1999; Kellner and Azevedo, 1999; Salgado and Azpilicueta,2000; Apesteguıa, 2004) and Maastrichtian (Bonaparte andPowell, 1980) demonstrate that sauropod dinosaurs attainedan amazing diversity in South America during the Cretaceous.

So far, few vertebrates have been found in South Americandeposits ranging in age from late HauterivianeBarremian (LaAmarga Formation; see Volkheimer, 1978; Montanelli, 1987;Chiappe, 1988; Salgado and Bonaparte, 1991; Leanza andHugo, 1995; Bonaparte, 1996) to early Cenomanian (Cande-leros Formation; see Calvo, 1999; Leanza and Hugo, 2001),a period of around 19 myr. The scarce materials of Chubuti-saurus insignis (Del Corro, 1975) and those of Rayososaurusagrioensis (Bonaparte, 1996), both from Aptian beds, are theonly sauropods known from this interval.

365J.F. Bonaparte et al. / Cretaceous Research 27 (2006) 364e376

In order to look for new remains of Aptian sauropods, oneof us (JFB) has led palaeontological fieldtrips in the NeuquenBasin, north-west Patagonia. In the Picun Leufu area, Dr. Hec-tor Leanza, working on a geologic map of the area, informedus of the existence of large reptile bones in the upper levels(Cullın Grande Member) of the Lohan Cura Formation. In1997, explorations of the Cerro de los Leones site (Fig. 1), lo-cated 10 km to the west of Picun Leufu, led to the discovery ofpart of an articulated skeleton of a new sauropod bearing largeosteoderms. This species was named Agustinia ligabuei (Bo-naparte, 1999b). During explorations carried out between1998 and 2000, three incomplete specimens of large sauropods

were discovered at Cerro Leon. One of these, the holotype ofa new genus and species named Ligabuesaurus leanzai is de-scribed herein. The other specimens are tentatively assigned tothe same species. Together with these sauropod remains,chelid turtles (identified by M. de La Fuente), theropod teethand isolated fragments of birds and crocodile bones were col-lected. This association indicates the existence of a new as-semblage of Early Cretaceous tetrapods for South America.

Most South American titanosaurs are represented by veryincomplete skeletal elements lacking cranial remains (e.g.,Andesaurus Calvo and Bonaparte, 1991; Aeolosaurus Powell,2003; Pellegrinisaurus Salgado, 1996; Argyrosaurus

Fig. 1. A, map of the Neuquen Basin (North Patagonia, Argentina). B, location of the area in South America. C, geological map of the Picun Leufu area showing

the locality where the holotype of Ligabuesaurus leanzai gen. et sp. nov. was found.

366 J.F. Bonaparte et al. / Cretaceous Research 27 (2006) 364e376

Lydekker, 1893; Argentinosaurus Bonaparte and Coria, 1993;Rocasaurus Salgado and Azpilicueta, 2000; LaplatasaurusHuene, 1929; Powell, 2003; Salgado, 2003). In this context,the new taxon described herein, comprising teeth and cranialmaterial associated with cervical and dorsal vertebrae, and gir-dle and limb bones, is relevant from a systematic and phyloge-netic point of view. Futhermore, dorsal vertebrae of this taxonshow an internal bone structure that is characterized by numer-ous cavities of the camellate type (sensu Wedel et al., 2000a).

2. Systematic paleontology

Institutional abbreviations. MACN-CH, Museo Argentinode C. Naturales, Buenos Aires, Argentina; MCF-PVPH, Mu-seo Carmen Funes, Paleontologıa de Vertebrados, Plaza Huin-cul, Neuquen, Argentina; YPM, Yale Peabody Museum, NewHaven, USA; IANIGLA-PV, Instituto Argentino de Nivologıa,Glaciologıa y Ciencias Ambientales, Coleccion Paleovertebra-dos, Mendoza, Argentina.

Saurischia Seeley, 1888Sauropodomorpha Huene, 1932Sauropoda Marsh, 1878Titanosauriformes Salgado, Coria and Calvo, 1997Titanosauria Bonaparte and Coria, 1993Ligabuesaurus gen. nov.

Type species. Ligabuesaurus leanzai sp. nov.

Derivation of name. In honour of Italian philanthropist andfriend Dr. Giancarlo Ligabue, and sauros (Greek), lizard,reptile.

Diagnosis. Large sauropod dinosaur characterized by thefollowing associated derived features: (1) laminar and antero-posteriorly compressed neural spines on posterior cervical andanterior dorsal vertebrae that are rhomboid in shape, and widerthan the vertebral centra; (2) spinoprezygapophyseal laminaein posterior cervical vertebrae forked to form two pairs of lam-inae: the medial pair unites them towards the top of the neuralspine, and the lateral pair form the lateral border of the neuralspine; (3) dorsoventrally reduced neural arch pedicels in theposterior cervical and anterior dorsal vertebrae; and (4) rudi-mentary prespinal lamina on the posterior cervical and anteriordorsal vertebrae.

Ligabuesaurus leanzai sp. nov.Figs. 2e7

Derivation of name. In honour of Dr. Hector Leanza, geo-paleontologist, colleague and friend, who informed us aboutthe palaeontological riches of Cerro Leon, Picun Leufu, Neu-quen Province.

Holotype. MCF-PHV-233, represented by the following as-sociated materials belonging to a single individual: an incom-plete maxilla with ten teeth, six cervical and dorsal vertebrae,

incomplete ribs, left and right scapulae, left humerus and prox-imal and distal parts of the right one, four left metacarpals anda right hind limb made of an incomplete femur, tibia, fibula,astragalus, five metatarsals and phalanges.

Horizon and locality. Finely stratified sandy and peliticlevels of the upper section (Cullın Grande Member) of the Lo-han Cura Formation, late AptianeAlbian (Leanza and Hugo,2001); Cerro Leon, 10 km to the north-west of Picun Leufu,Neuquen Province.

Diagnosis. As for genus.

Comparative description

Maxilla (Fig. 2A). The incomplete right maxilla has a se-verely worn external surface, and there is no sign of antorbitalfossa, preantorbital foramen, or any other foramina, or of a pal-atal shelf on the medial side. The dorsal ascending process arisesfrom the dorsal border of the maxillary bone and follows the lineof the premaxillary contact. The ascending process is wide, an-teroposteriorly extended with four robust teeth present beneath.The preserved portion does not reach the lacrimal overlappingzone or the medial process of the narial floor. The premaxilla-maxilla contact is not clear but can be deduced from the obliqueanterodorsal margin of the bone, which is similar to that of othersauropod maxillae (e.g., Brachiosaurus, Camarasaurus, Di-plodocus, Euhelopus, Nemegtosaurus).

The jugal (posteroventral) process is poorly preserved andbears five teeth. As preserved, this process is low and posteri-orly directed (instead of posterodorsally as in RapetosaurusCurry Rogers and Forster, 2004), resembling the conditionseen in Euhelopus. Both the dorsal and ventral margins ofthe jugal process taper backwards. It is not possible to deter-mine if the articulation of the maxilla and jugal is ‘‘tongue-in-groove’’ as in Rapetosaurus or if there is a dorsoventrallyextensive jugal facet that overlaps the posterior border of themaxilla, as in Brachiosaurus, Camarasaurus, Diplodocus, Eu-helopus, Nemegtosaurus, and Quaesitosaurus.

The maxilla bears ten equally spaced teeth in their originalposition along the straight alveolar margin of the maxilla. Asin basal sauropods and other primitive titanosaurs (e.g., Martı-nez, 1998), teeth in Ligabuesaurus are not restricted to the an-terior part of the maxilla. The teeth (Fig. 2B) have cylindricalroots and rather labiolingually compressed cone-chisel-likecrowns (sensu Calvo, 1994). The crowns are mesodistally con-vex labially and concave lingually. Their diameter is not largerthan that of the root. These teeth are different from those ofCamarasaurus, bearing a strong central axis with a single lat-eral expansion or wing. They are similar to those of Brachio-saurus (Janensch, 1950; Calvo, 1994), sharing with it and withderived titanosaurs the perpendicular orientation of the toothaxis with respect to the alveolar margin, and the presence ofsharply inclined wear facets, a synapomorphic feature for Ti-tanosauriformes sensu Salgado and Calvo (1997). The wearfacets are comma-shaped, better developed at the tip of the

367J.F. Bonaparte et al. / Cretaceous Research 27 (2006) 364e376

tooth, and descending over the single wing of the crown, thusbeing sharply inclined with respect to the labiolingual axis.

Wilson and Sereno (1998) described the absence of denti-cles in derived neosauropods, such as Diplodocidae and Tita-nosauridae. However, in more primitive forms, the enamelextension over the crown edges may develop pseudo-denticles.In Ligabuesaurus some of these secondary denticles are pre-served only on the apex of a single tooth. The enamel is, asin most Eusauropoda, profusely sculptured, showing a dendriti-cally rugose pattern, often recorded in some isolated teeth re-ferred to Titanosauria (Powell, 2003).

Posterior cervical vertebrae (Fig. 3, Table 1). One posteriorcervical or cervicodorsal vertebra has been recovered. It israther complete, lacking only the posterior half of the centrum,the left diapophysis and part of the right. Its vertebral centrumis dorsoventrally depressed, being wider than tall. A smalltriangle-shaped, deep pleurocoel is located approximately inthe middle of the centrum and near the ventral border.

The parapophyses are very robust and project anterolater-ally. On the dorsal face of the parapophysis, there is a poster-omedial concavity that extends down to the centrum, formingsome kind of pneumaticoel with two depressions, a shallowdorsal one and a deeper ventral one.

Both pre and postzygapophyses are relatively low in posi-tion, close to the dorsal border of the centrum. The pre- andpostzygapophyses are widely separated from each other, ex-ceeding transversely the width of the centrum. The pedicelsof the neural arch are very short (Fig. 3C). The neural archis low on the mid and anterior centrum area, whereas it be-comes tall backwards where the neural spine is located.

The transverse process is well-developed and the laminathat connects it to the prezygapophysis, the prezygodiapophy-seal lamina, forms a wide dorsal plane (Fig. 3A). This planeextends backwards from the diapophysis, being ventrally lim-ited by the postzygodiapophyseal lamina, by the

Fig. 2. Ligabuesaurus leanzai, MCF-PVPH-233. A, right maxilla in medial

view. B, isolated tooth. Abbreviations: psd, pseudodenticles; wf, wear facet;

lf, lateral flange; cc, central column.

spinopostzygapophyseal lamina at the back, and dorsally bythe lateral expansion of the spinoprezygapophyseal lamina.Ventrally, the diapophysis has two centrodiapophyseal laminaethat reach the centrum, surrounding a wide, deep medial cav-ity. Another wide, triangle-shaped cavity is defined by the pos-terior centrodiapophyseal and postzygodiapophyseal laminae,resembling that observed in the cervical vertebrae of Sauropo-seidon proteles and Brachiosaurus brancai (Wedel et al.,2000b). Forward with respect to the anterior centrodiapophy-seal lamina, there is a brief depression anteriorly borderedby a thick centroprezygodiapophyseal lamina.

In anterior view (Fig. 3C) a wide, nearly horizontal intra-prezygapophyseal lamina is observed connecting both prezy-gapophyses, forming a roof for the neural canal. This

Table 1

Measurements (in cm) of the vertebrae of Ligabuesaurus leanzai

Material Total

height

Total

width

Width, height

and length of

the neural

spine

Transverse

width of the

centrum

Posterior cervical

(MCF-PVPH-233/2)

68 66 (est: 111) 43e42e11 35

Anterior dorsal

(MCF-PVPH-233/3)

80 77 (est: 100) 43e45e9 38

Posterior dorsal

(MCF-PVPH-233/4)

88 54 (est: 60) 25e27e8 30

est, Total estimated.

Fig. 3. Ligabuesaurus leanzai, MCF-PVPH-233. Posterior cervical vertebra in

A, lateral, G, posterior, and C, anterior views. Abbreviations: acdl, anterior

centrodiapophyseal lamina; cpol, centropostzigapophyseal lamina; cprl, cen-

troprezygapophyseal lamina; dia, diapophysis; lsprl, lateral spinoprezygapo-

physeal lamina; msprl, medial spinoprezygapophyseal lamina; pa,

parapophysis; pcdl, posterior centrodiapophyseal lamina; podl, postzygadiapo-

physeal lamina; poz, postzygapophysis; prdl, prezygadiapophyseal lamina;

prz, prezygapophysis; spol, spinopostzygapophyseal lamina; tprl, intraprezy-

gapophyseal lamina. Scale bar represents 10 cm.

368 J.F. Bonaparte et al. / Cretaceous Research 27 (2006) 364e376

lamina, together with the spinoprezygapophyseal laminae,form a depressed triangle-like structure.

The neural spine is located in the posterior area of the neu-ral arch and is inclined backwards. It is laminar, anteriorlyconvex and posteriorly concave, and in anterior and posteriorviews it is broad and rhomboidal (Fig. 3B, C). This type ofneural spine clearly differs in size and morphology from thecervical and anterior dorsal spines of Brachiosaurus brancai(Janensch, 1950) and other Jurassic sauropods like Diplodocus(Marsh, 1877), Camarasaurus (Cope, 1877; McIntosh et al.,1996), and the known titanosauriforms (Salgado et al., 1997a).

The spinoprezygapophyseal lamina is forked to form twolaminae: (1) a medial spinoprezygapophyseal lamina, whichcontacts with its pair near the distal end of the neural spine,and (2) a lateral spinoprezygapophyseal lamina, which formsthe lateral rhomboidal border of the neural spine (Fig. 3C).The presence of these laminae is considered here as a possibleautapomorphy of Ligabuesaurus. On the posterior face of theneural spine (Fig. 3B) the spinopostzygapophyseal laminae arewell developed, and continue towards the end of the neuralspine but not along the outer borders.

The neural spine differs from the cervical and anterior dor-sal neural spines of Isisaurus colberti (Jain and Bandyopad-hyay, 1997; Wilson and Upchurch, 2003), not only in theirshape but also in their structure, laterally expressed by the spi-nopostzigapophyseal or spinodiapophyseal laminae.

The neural spines of Ligabuesaurus also differ from thecervical neural spines assigned to Mendozasaurus (GonzalezRiga, 2005). Mendozasaurus shares with Ligabuesaurus thepresence of neural spines that are wider transversely than thevertebral centra. However, the neural spines of Mendozasaurusare ‘‘fan-like’’ in shape due to lateral expansions that are notconnected with lateral spinoprezygapophyseal laminae, as oc-curs in Ligabuesaurus cervical vertebrae. In Mendozasaurusthe lateral spinoprezygapophyseal laminae are absent (IA-NIGLA-PV 076) and the only pair of spinoprezygapophyseallaminae runs toward the medial plane of the neural spine.

Anterior dorsal vertebra (Fig. 4, Table 1). This vertebra isrelatively complete, except for the prezygapophysis. It is ante-roposteriorly deformed and its internal structure is composedof abundant, irregularly sized cavities, and a remarkably thinperiostium (ca. 1e3 mm thick). The centrum is opisthocoe-lous, relatively wide and low, hardly reaching 28% of theheight of the vertebra. The long and robust diapophysis pro-jects laterally. The infradiapophyseal area is reduced owingto the relatively low position of the diapophyses and the dor-soventrally reduced pedicels of the neural arch. This trait isconsidered an autapomorphy of Ligabuesaurus.

In the infradiapophyseal area there are two laminae fromthe diapophyses to the parapophyses. The neural spine is trans-versely well developed, exceeding the width of the centrum. Itis laminar, exhibiting a rhomboidal shape in anterior and pos-terior views. Although both Brachiosaurus brancai (Janensch,1950) and Argentinosaurus huinculensis (Bonaparte and Coria,1993) show anteriorly rhomboidal dorsal neural spines, theyboth have a less transverse development and are considerably

thicker anteroposteriorly. Because of this, the flat neural spinecould be autapomorphic for Ligabuesaurus.

The anterior region of the neural spine shows, as in the pos-terior cervical, well-developed and forked spinoprezygapo-physeal laminae, which converge dorsally toward the axialplane, forming a thick, low medial strip of bone, thus differingfrom the well-developed lamina present in Brachiosaurusbrancai (Janensch, 1950) and most derived titanosaurs. Thepresence of this low strip of bone suggests a stage of incipientdevelopment of the prespinal lamina.

The posterior side of the neural spine is remarkably similarto the anterior one, having spinopostzygapophyseal laminaewhich tend to converge dorsally towards the axial plane butwithout fusing with each other, forming a low incipient post-spinal lamina.

The postzygapophyseal articular facets are elliptical andventrolaterally orientated. A wide, deep space is present be-tween both postzygapophyses. The hyposphene-hypantrum ac-cessory articulations are absent in this vertebra, but they arepresent in the posterior dorsal vertebrae.

Posterior dorsal vertebrae (Fig. 5, Table 1). Four posteriordorsal vertebrae, forming two clusters of two, have been re-covered. They are similar to the preceding vertebrae, differingmainly in the presence of a hyposphene, which is partially pre-served on the posterior side of the neural arch on one of them,although incomplete and anteroposteriorly deformed. Theopisthocoelous centrum is low and wider than tall. On the an-terior side (Fig. 5), the neural spine shows a low, wide, incip-ient prespinal lamina, more developed than that observed inthe anterior dorsal vertebrae.

The vertebrae are strongly opisthocoelous with centra ofvariable length, apparently varying with the position on the se-ries (they are long in one cluster, and short in the other) andwith camellate internal structure. The diapophyses are not

Fig. 4. Ligabuesaurus leanzai, MCF-PVPH-233. Anterior dorsal vertebra in A,

anterior and B, lateral views. Abbreviations: cprl, centroprezygapophyseal

lamina; dia, diapophysis; pa, parapophysis; poz, postzygapophysis; posl, incip-

ient postspinal lamina; prz, prezygapophysis; sprl, spinoprezygapophiseal lam-

ina; spol, spinopostzygapophyseal lamina. Scale bar represents 20 cm.

369J.F. Bonaparte et al. / Cretaceous Research 27 (2006) 364e376

preserved. Nevertheless, the centrodiapophyseal lamina isforked in an anterior and a posterior laminae, just as in the ti-tanosaur cf. Argyrosaurus (MACN-CH 217, Bonaparte,1999a). The neural spines are inclined backwards.

In all the recovered dorsal vertebrae, the periostium is verythin, only reaching 2 mm in some places (e.g., prezygapophysealprocess), and 3e4 mm near to the zygapophyses. The periostiumis only 0.8e1 mm in thick in the extensive flat areas of the neuralarch and vertebral centrum. Below the periostium, variouslysized macrocells are observed, most ranging from 8 to 25 mm,but sometimes considerably larger. Similar bony structureshave been described and figured in sauropods from the Early Cre-taceous of Croatia (Dalla Vecchia, 1998) and North America(Wedel et al., 2000a,b), and in the saltasaurine titanosaur Salta-saurus from the latest Cretaceous of Argentina (Powell, 1992).

Scapula (Fig. 6B, Table 2). The relatively complete scapu-lae show widely expanded proximal regions. The acromial de-pression is more reduced than in Brachiosaurus brancai(Janensch, 1950, pl. 15, figs. 1, 2). At the ventral surface ofthe proximal end, close to the glenoid area, a prominent lam-inar process is present, which is not observed in Brachiosaurusbrancai and differs from the ‘‘medial process’’ described inSaltasaurus (Powell, 1992, fig. 28). Near the glenoid cavityand on the same ventral border, another smaller, but robustprocess is present. The scapular blade is distally reduced asin most titanosaurs, lacking the distal expansion present inBrachiosaurus brancai (Janensch, 1950, pl. 15, fig.1). The gle-noid cavity of Ligabuesaurus, as well as in Euhelopus and theTitanosauria (e.g., Opisthocoelicaudia, Saltasaurus), is medi-ally inclined, while the coracoid area is laterally exposed, a de-rived character state that is also present in Somphospondyli(Wilson and Sereno, 1998). In Camarasaurus and Brachiosau-rus, the scapular glenoid region is laterally more expanded.The transverse section of the scapular blade is laterally convex

Fig. 5. Ligabuesaurus leanzai, MCF-PVPH-233. Posterior dorsal vertebra in

anterior view. Abbreviations: cprl, centroprezygapophyseal lamina; prel, incip-

ient prespinal lamina; prz, prezygapophysis; spdl, spinodiapophyseal lamina.

Scale bar represents 10 cm.

and slightly concave internally, as in Patagosaurus, Chubuti-saurus and Antarctosaurus, among others.

Humerus (Fig. 6A, Table 2). A complete left humerus andthe proximal and distal portions of the right one have been re-covered. It is a proportionally slender bone, with a very narrowdiaphysis (18 cm in diameter) and only slightly expanded onits proximal region, as in Brachiosaurus. The humerus/femurratio is 0.9, very similar to the proportions of Brachiosauridaesensu McIntosh (1990). The proximal end shows a thick me-dial portion, which includes the humeral head, relativelymore developed than in both species of Brachiosaurus (Riggs,1903, pl. 74, fig.3; Janensch, 1950, fig. 1). The proximolateralportion, however, is very thin. There is a prominent deltopec-toral crest, developed only in the proximal third of the hu-merus, in a position slightly more dorsal than inBrachiosaurus. The posterior face of the humerus showsa prominent, nearly spherical, humeral head, which resemblesthat of Brachiosaurus altithorax (Riggs, 1903), but it is moredeveloped than in Brachiosaurus brancai (Janensch, 1950).This character has not been observed in other Titanosauria(sensu Salgado et al., 1997a,b). In the distal region, the inter-nal supracondylar crest is prominent.

Metacarpals (Table 2). From the four available metacarpals,only two (II and III) are complete. They exhibit relatively slen-der proportions, with flat and triangular proximal ends, in whichrough surfaces indicate the zones for cartilage attachment. Thelargest side is developed on the anterior or external face. Threeof these bones show slightly convex, densely pitted and rougharticulation surfaces on the distal end, as in Chubutisaurus andother titanosaurs. The remaining metacarpal, however, exhibitsa strongly concave articulation surface, comparable to that ofBrachiosaurus (Janensch, 1950), suggesting the presence ofa well-developed phalanx. The humerus/metacarpal III ratio is

Fig. 6. Ligabuesaurus leanzai, MCF-PVPH-233. A, left humerus in posterior

and anterior views. B, scapula in lateral view. Abbreviations: cd, crista delto-

pectoralis; gl, glenoid zone; hh, humeral head; pap, postacromial process; rc,

radial condyle; uc, ulnar condyle; vmp, ventromedial process. Scale bar repre-

sents 50 cm.

370 J.F. Bonaparte et al. / Cretaceous Research 27 (2006) 364e376

around 31% for Ligabuesaurus, very close to that of Brachiosau-rus brancai ratio (Janensch, 1950).

Right hind limb

Femur (Fig. 7A, Table 2). The right femur has an incom-plete proximal end, lacking a substantial portion of the femo-ral head. Along the proximolateral border, a slight lateralprotuberance stands out, as in Brachiosaurus, Chubutisaurus,Austrosaurus, Aegyptosaurus, Phuwiangosaurus and most tita-nosaurs (Janensch, 1950; Salgado, 1993; Salgado and Calvo,1997; Wilson and Sereno, 1998). This character was consid-ered by Salgado et al. (1997a) to diagnose the Titanosauri-formes and interpreted to be related to a redistribution of thecorporal mass in basal Titanosauriformes. Later, Wilson andCarrano (1999) studied the mechanics and ichnological recordof this feature, functionally associating the femoral lateralbulge with the distal condylar asymmetry.

In titanosauriforms such as Chubutisaurus, Ligabuesaurus,and derived titanosaurs, the femur exhibits an anteroposteriorcompressed section that apparently compensated the eccentricloading of the femur shaft imposed by the parasagittal stance(Wilson and Carrano, 1999). The wide distal end is relativelymore symmetrical than in Camarasaurus (Cope, 1877), Mamen-chisaurus (Young, 1954), and Apatosaurus (Marsh, 1877), thusbeing similar to Brachiosaurus brancai (Janensch, 1950) andPhuwiangosaurus sirindhornae (Martin et al., 1994, 1999).The femoral head, although incomplete, seems to have been lo-cated above the level of the larger trochanter, as in Brachiosau-rus altithorax (Riggs, 1903) and Phuwiangosaurus. The fourthtrochanter is located in the proximal half of the femur.

Tibia, fibula and astragalus (Fig. 7B, Table 2). The tibiaand fibula are both proportionally slender and long, represent-ing 66% of the femur length, a larger ratio than that observedin Brachiosaurus brancai (Janensch, 1950). The cnemial crestis curved anterolaterally, as in all Eusauropoda (Wilson andSereno, 1998). The proximal surface of the tibia is subcircular,

Fig. 7. Ligabuesaurus leanzai, MCF-PVPH-233. A, right femur in anterior

view. B, articulated right tibia, fibula and astragalus in posterior view. C, artic-

ulated right metatarsals in proximal and posterior views. Abbreviations: ast,

astragalus; cc, cnemial crest; fc, fibular condyle; lb, lateral bulge; tc, tibial con-

dyle. Scale bar represents 50 cm in A and B, 12 cm in C.

with the anteroposterior diameter larger than the transverseone. At the middle of its length the diaphysis is thin. Distallythere is a marked lateral expansion to house the astragalus.The longer axis of the distal end is mainly transverse, withthe external border in a more posterior position than the inter-nal one, a character assigned by Salgado et al. (1997a) to their‘‘Unnamed taxon 1’’ (Chubutisaurusþ Titanosauria).

The fibula is substantially longer than the tibia and both endsare slightly expanded. The proximal end is anteroposteriorlysquared in shape, and the distal end is nearly circular, with an ob-lique longer axis, from the posterolateral to anteromedial sides.The fibular process is not well marked and is located near thehalf length of the fibula. The astragalus is smaller than the distalend of the tibia. It shows a wide, concave lateral side, and a dor-soventrally wide, posterolateral border.

Pes (Fig. 7C, Table 2). The right pes includes the five meta-tarsals that were found in an approximately articulated posi-tion. The proximal and distal articular surfaces, althoughwell defined, are rough because of the thick cartilaginouscover. Metatarsal I shows a wide, laterally projected, distalend. It is clearly articulated to a small proximal phalanx,which is continued by an ungual phalanx larger than the meta-tarsal. The proximodistal length of metatarsal I is only slightlylonger than the transverse width of the distal end.

Metatarsal I is proportionally shorter than in Diplodocuslongus (YPM 1920) and its medial side is not so curved,thus being more similar to Camarasaurus grandis (YPM1901) or Antarctosaurus wichmannianus (Huene, 1929). Theproximal region of this metatarsal, as in Janenschia robusta(Bonaparte et al., 2000), is not as medially developed as in Di-plodocus, Camarasaurus or even Antarctosaurus. It lacks theproximolateral process of Camarasaurus (Cope, 1877). Thedistal end is wide and projected laterally. The condyle isstrongly divided on its ventral side, as occurs in Antarctosau-rus. In both Janenschia and Antarctosaurus, the medial con-dyle is smaller than the lateral, perhaps related to thepresence of a small pre-ungual phalanx. In Ligabuesaurus,as in Antarctosaurus, the articulation for metatarsal II, onthe posterolateral side, is wide, framed by a diagonal ridgethat runs laterodistally along the posterior face of metatarsal I.

Table 2

Measurements (in cm) of the appendicular bones of Ligabuesaurus leanzai

Material Length Minimum

width

Maximum

distal width

Maximum

proximal width

Scapula 144 21 41(1) ?(2)

Humerus 149 18 41 40

Metacarpal III 48 7 14 13

Femur 166 25 45 37

Tibia 104 9 25 27

Fibula 108 8.5 16 20

Metatarsal I 14 6 12 13

Metatarsal II 19 5.5 10 14

Metatarsal III 22 5 10 12

Metatarsal IV 22 5.5 9 12.3

Metatarsal V 18 5.5 7.5 15.5

(1), Maximum distal width perpendicular to the axis of the scapular blade.

(2), Maximum acromion width, oblique at 50 � from the blade axis.

371J.F. Bonaparte et al. / Cretaceous Research 27 (2006) 364e376

Metatarsal II is a bit longer, with a proximal extensive an-teroposterior region, and a wide distal articular area. Metatar-sal III is only 1 cm longer than metatarsal II, and possessesa proportionally thinner diaphysis. Metatarsal IV is a bitshorter than the previous one, with a thicker diaphysis. Meta-tarsal V has a wide proximal region that is highly laminar as inother sauropods. The distal end is smaller than in the remain-ing metatarsals.

3. Brief comments on the phylogenetic relationshipsof Ligabuesaurus leanzai

The partially articulated specimen of Ligabuesaurus leanzaicontributes substantially to knowledge of titanosauriform evolu-tion during the Early Cretaceous in South America. It providesinformation about those taxa bearing several ‘‘brachiosaurid’’characters, which can now be considered as basal titanosaurs.

The phylogenetic relationships among Ligabuesaurus andother sauropods were studied through a cladistic analysisbased on 80 characters corresponding to 20 taxa (see Appen-dix). Patagosaurus fariasi (Bonaparte, 1979, 1986), Jobaria ti-guidensis (Sereno et al., 1999) and Diplodocus carnegii(Hatcher, 1901; McIntosh, 1990) were considered as succes-sive outgroups, and the ingroup includes Camarasaurus gran-dis (Cope, 1877), Brachiosaurus brancai (Janensch, 1950),Chubutisaurus insignis (Del Corro, 1975), Phuwiangosaurussirindhornae (Martin et al., 1994, 1999; Upchurch, 1999), An-desaurus delgadoi (Calvo and Bonaparte, 1991), Malawisau-rus dixeyi (Jacobs et al., 1993), Mendozasaurus neguyelap(Gonzalez Riga, 2003, 2004, 2005), Isisaurus colberti (Jainand Bandyopadhyay, 1997; Wilson and Upchurch, 2003), Ra-petosaurus krausei (Curry Rogers and Forster, 2001), Liraino-saurus astibiae (Sanz et al., 1999), Aeolosaurus rionegrinus(Salgado and Coria, 1993; Salgado et al., 1997b; Powell,2003), Opisthocoelicaudia skarzynskii (Borsuk-Bialynicka,1977), Alamosaurus sanjuanensis (Gilmore, 1946), Neuquen-saurus australis (Huene, 1929; Powell, 2003; Salgado et al.,in press), Saltasaurus loricatus (Bonaparte and Powell,1980; Powell, 1992), Rocasaurus muniozi (Salgado and Azpi-licueta, 2000) and Ligabuesaurus leanzai.

The data matrix was run using the program NONA, version2.0 (Goloboff, 1993), and the character polarity was deter-mined by comparison with the outgroup. The multi-state char-acters were considered unordered. Two most parsimoniouscladograms were obtained, with relatively high indices (148steps, consistency index, 0.63; retention index, 0.75).

The robustness of nodes were estimated by bootstrap andjack-knife values. The basal nodes 3, 4 and 5 (Titanosauri-formes, Somphospondyli and Titanosauria) and the more de-rived taxa (nodes 12, 13 and 14) obtained the highest valuesand are relatively well supported. In contrast, the other nodesare weakly supported due to the missing data. The strict con-sensus cladogram shows an unresolved polytomy betweenLigabuesaurus and Phuwiangosaurus (Fig. 8).

Although the cladogram obtained bears some similarities tothose of previous studies (Salgado et al., 1997a; Wilson andSereno, 1998; Upchurch, 1999; Wilson, 2002), it also shows

some novelties that add to our knowledge of basal titanosaurevolution. This is discussed here in a preliminary way.

Titanosauriformes (node 3) was originally defined by Sal-gado et al. (1997a, p. 12) as ‘‘the most recent common ancestorof Brachiosaurus brancai, Chubutisaurus insignis and Titano-sauria and all of its descendants’’. Later, several authors rede-fined this clade based on other phylogenetic criteria (seeWilson and Sereno, 1998; Sereno, 1998). In our analysis, Tita-nosauriformes is supported by five unambiguous synapomor-phies: compressed cone chisel-like teeth (11.2); neural archesplaced anteriorly in middle and posterior caudal centra (49.1);preacetabular lobe of the illium expanded and dorsally directed(73.1); pubic peduncle of the ilium perpendicular to the sacralaxis (75.1); and lateral bulge of the femur below the greater tro-chanter (78.1). With respect to the original diagnosis of Titano-sauriformes proposed by Salgado et al. (1997a), the presence ofcompressed cone, chisel-like teeth (1.2) is added in this analysis.

The presence of prespinal lamina in dorsal neural spines(character 34), cited originally as a synapomorphy of Titanosau-ria, exhibits variable development. In basal titanosauriforms,this feature is present only on the distal end of the neural spine(e.g., Brachiosaurus) or is well developed up to the base of theneural spine (e.g., Chubutisaurus). In contrast, in Phuwiango-saurus it is absent and in Ligabuesaurus it appears as an incipi-ent prespinal lamina. In derived titanosaurs it is well developedup to the base of neural spine, except in Andesaurus and Mala-wisaurus. For this reason, the presence of a prespinal lamina onthe distal end of the neural spine (character 34 state 2) should beexcluded from the diagnosis of Titanosauriformes until furtherstudies clarify the nature and states of this feature.

Ligabuesaurus shares with the basal titanosauriformBrachiosaurus, the development of relatively long fore-limbs,reaching a humerus/femur ratio value of 0.9. Although this char-acter has been proposed as a synapomorphy of Brachiosauridae(McIntosh, 1990), this analysis shows that it is also present inother non-brachiosaurid titanosauriforms. The relatively longfore-limbs are here interpreted as a parallel acquisition relatedto adaptative functions, or as a plesiomorphic condition of Tita-nosauriformes retained in basal titanosaurs, being also present,although less developed, in Chubutisaurus, a titanosauriformwith a humerus/femur ratio of 0.86 (Salgado, 1993).

Somphospondyli (node 4) was defined by Wilson and Sereno(1998, p. 53) as ‘‘titanosauriforms more closely related to Salta-saurus than to Brachiosaurus’’. In our analysis, this clade in-cludes Chubutisaurus, Phuwiangosaurus, Ligabuesaurus andall titanosaurs. It is diagnosed by three unambiguous synapomor-phies: presacral vertebrae with camellate or somphospondylousinternal bone structure (40.1); scapular glenoid deflected medi-ally (59.1); and distal end of tibia transversely expanded (79.1).

Titanosauria (node 5), originally named by Bonaparte andCoria (1993), was phylogenetically defined by Salgado et al.(1997a, p. 18) as ‘‘the most recent common ancestor of Ande-saurus delgadoi, Titanosauridae and all their descendants’’.Later, Sereno (1998, p. 63) redefined Titanosauria througha stem-based definition, as ‘‘all somphospondylians closer toSaltasaurus than to Euhelopus’’. Salgado (2003) followedthe redefinition of Sereno. Finally, Wilson and Upchurch

372 J.F. Bonaparte et al. / Cretaceous Research 27 (2006) 364e376

Fig. 8. Cladogram showing the phylogenetic relationships of Ligabuesaurus leanzai based on strict consensus of two most parsimonious trees (148 steps, consis-

tency index: 0.63, retention index: 0.75). Synapomorphies are listed and discussed in the text. The robustness of nodes Titanosauriformes, Somphospondyli, Ti-

tanosauria and Saltasaurinae are indicated in brackets (bootstrap and jackknife values, respectively).

(2003) adopted the original definition proposed by Salgadoet al. (1997a) as a node-based grouping. These differentdefinitions of Titanosauria have important consequences inthe interpretation of the phylogenetic relationships of Ligabue-saurus and other basal titanosaurs.

Following the stem-based definition (Sereno, 1998; Salgado,2003) Ligabuesaurus and Phuwiangosaurus are included withinTitanosauria and considered as basal titanosaurs less derivedthan Andesaurus. In this case, Titanosauria is supported byfive synapomorphies defined by delayed optimization: presenceof centroparapophyseal lamina in the posterior dorsal vertebrae(35.1); ventrally widened centrodiapophyseal laminae in poste-rior dorsal vertebrae (36.1); acuminate (eye-shaped) pleurocoelsin dorsal vertebrae (39.1); pubis longer than ischium (69.1); andrelatively short posterior process of the ischium with respect tothe length of the pubis articulation (71.1). The first four charac-ters were originally proposed by Salgado et al. (1997a) and thelast one is added in this paper.

The phylogenetic relationships between Ligabuesaurus,Phuwiangosaurus and Andesaurus are poorly understood be-cause some cranial, cervical and caudal characters of thesetaxa are unknown. In this preliminary analysis, Ligabuesaurusforms a polytomy with Phuwiangosaurus. In one cladogram,Ligabuesaurus appear as a sister taxon of Phuwiangosaurus,sharing the presence of a shallow or reduced supradiapophy-seal fossa on the cervical vertebrae (24.1). In the other clado-gram, Ligabuesaurus appears as a taxon that is less derived

than Phuwiangosaurus. In both cases, Ligabuesaurus and Phu-wiangosaurus are less derived titanosaurs than Andesaurus.Similarly, Allain et al. (1999) and Upchurch (1998, 1999) con-sidered that Phuwiangosaurus sirindhornae from Thailand andTangvayosaurus hoffeti from Laos are basal titanosaurs.

This phylogenetic analysis sheds some light on the uncer-tain relationships of the basal titanosaurs, and provides evi-dence that both the phylogenetic definition and the diagnosisof Titanosauria should be re-evaluated in the framework ofthe recently discovered taxa, which include Ligabuesaurus,Andesaurus, Phuwiangosaurus and Tangvayosaurus.

4. Discussion and conclusions

Ligabuesaurus leanzai is a new titanosaur from the LowerCretaceous (Upper AptianeAlbian) of Neuquen Province, Pa-tagonia. Probable autapomorphies of this species are: (1) lam-inar and anteroposteriorly compressed neural spines ofrhomboid shape on the posterior cervical and anterior dorsalvertebrae that are wider than the vertebral centra; (2) spinopre-zygapophyseal laminae in the posterior cervical vertebraeforked to form two pairs of laminae: the medial pair unites to-wards the top of the neural spine, and the lateral pair forms thelateral border of the neural spine; (3) dorsoventrally reducedneural arch pedicels in the posterior cervical and anterior dor-sal vertebrae; (4) rudimentary prespinal lamina on the poste-rior cervical and anterior dorsal vertebrae.

373J.F. Bonaparte et al. / Cretaceous Research 27 (2006) 364e376

A preliminary phylogenetic analysis suggests that Ligabue-saurus is a basal titanosaur. It exhibits derived features of Ti-tanosauriformes such as compressed cone-shaped, chisel-liketeeth and a lateral bulge of the femur below the greater tro-chanter. Other derived characters of Titanosauriformes un-known in Ligabuesaurus are: neural arches located anteriorlyin the middle and posterior caudal vertebrae; preacetabularlobe of illium expanded and dorsally directed; and pubic pe-duncle of the ilium perpendicular to the sacral axis.

Ligabuesaurus bears derived characters of Titanosauria sensuthe phylogenetic definition of Sereno (1998) and Salgado (2003):acuminate (eye-shaped) pleurocoels in the dorsal vertebrae; cen-trodiapophyseal laminae ventrally widened or lightly forked inthe posterior dorsal vertebrae; and presence of centroparapophy-seal laminae in posterior dorsal vertebrae. Although these char-acters place Ligabuesaurus within Titanosauria, some otherfeatures, such as the dorsoventral reduction of the base of the dor-sal neural arches, the incipient nature of the pre- and postspinallaminae and the laminate condition of the neural spine, suggestthat the definition of Titanosauria is not yet complete.

Acknowledgements

We thank the Centre Studi Ricerche Ligabue, Venice, Italy,for supporting fieldwork; the Garcıa Crespo family, farmowners, for generous cooperation; Professor Rodolfo A. Coria,Director of the ‘‘Carmen Funes’’ Museum, Plaza Huincul, Neu-quen, for formal and effective cooperation; Agustın Martinelli,Daniel Hernandez and Mr. Ricardo for fieldwork and specimenpreparation; Stella M. Alvarez, Yamila Gurovich, Lorena Case-lla, and Rodrigo Paz for their valuable cooperation in the field; Y.Gurovich for improving our English; the authorities of the Mu-seo Argentino de Ciencias Naturales for general support and fa-cilities; and finally the referees for their helpful comments.

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Appendix

Characterization matrix

In the Character-Taxon Matrix below the distribution of 80 characters corresponding to 20 sauropod taxa is shown. Characters 11, 33, 34, 40, 54 and 55 were

modified or redefined. The authors of the characters are indicated in the list of characters.

Taxon Characters

1e10 11e20 21e30 31e40 41e50 51e60 61e70 71e80

Patagosaurus fariasi 0????????? 000?000000 000000?000 0000000000 0?0?000000 0000000000 000000?000 0000000000

Jobaria tiguidensis 1111010000 ??01110000 0001000000 000?1?0100 0000000000 0000?00??0 ?0??00000? ???0?0?0?0

Diplodus longus 1011011100 1112110001 1102112010 0003100100 0100000001 1000000000 0000000000 0000001000

Camarasaurus grandis 0111010100 0100110001 1000000110 0010000100 0000000000 0010000100 0000011001 0000001000

Brachiosaurus brancai 0111010000 2001110000 0000100100 0012000100 00?0000010 0010000100 0000011001 0010111100

Chubutisaurus insignis ?????????? ?????????? ???????1?? ???3?00101 ?0??000010 ?0????0?10 0????1?0?? ?????1?11?

Phuwiangosaurus sirindhornae ?????????? ????1100?1 10010??1?0 0?101?011? ????000010 001???0110 0?100??011 11101011??

Ligabuesaurus leanzai ?????????? 200?11010? 000100?101 0011110111 ?????????? ????????10 0???0??0?? ?????111??

Andesaurus delgadoi ?????????? ?????????? ???????10? 1012110111 ?0??001010 00101001?0 ?????1??11 10???0?1??

Malawisaurus dixeyi 0?1??????? 300?000000 00001??10? 1??2111111 ???0002010 10101101?? ?1210?1??1 10??????11

Mendozasaurus neguyelap ?????????? ????10010? 001220??00 ???3???111 ???0002110 1010110110 1121?111?? ?????01111

Isisaurus colberti ?????????? ????100000 001220?100 ?003011111 1???002210 1010000110 01?00?1?11 11111??1??

Rapetosaurus krausei 1000001111 3012100000 00001?1101 11031?1111 1?1000221? ?0100?0110 1120010?11 11111011?1

Lirainosaurus astibiae ?????????? 30???????? ???????10? 1013111111 ?1??002210 10?0?00??0 1?201????? ??????11?1

Aeolosaurus rionegrinus ?????????? ?????????? ????????0? ???3???11? ?3??002210 10100101?? 1?20?1?111 01????11?1

Opisthocoelicaudia skarzynski ?????????? ?????????? ?0???01111 11031?1111 1211000010 1010000111 1120111111 11??101110

Alamosaurus sanjuanensis ????0????? 3?1?10?0?0 00001??10? 110?0?11?? 1311012210 1110000110 11211111?1 12111??1?0

Neuquensaurus australis ?????????? ????101000 000?0??101 1103111111 13??112210 1101000110 11201????1 12111?1111

Saltasaurus loricatus ???10?0101 301?111010 000101?101 1103111111 11??112210 1101001111 212011?111 1211101111

Rocasaurus muniozi ?????????? ?????????? ??010??101 1103111111 ????112210 1101001??? ????????11 12111??1??

List of characters

1. External nares, position: retracted to level of the orbits (0); retracted to

a position between orbits (1) (Upchurch, 1999).

2. External nares, maximum diameter: shorter (0) or longer (1) than orbital

maximum diameter (Wilson and Sereno, 1998).

3. Lacrimal anterior process: present (0); absent (1) (Wilson, 2002).

4. Frontal contribution to supratemporal fossa: present (0); absent (1)

(Wilson and Sereno, 1998).

5. Frontals, midline contact (symphysis): sutured (0) or fused (1) in adult

individuals.

6. Parietal occipital process, dorsoventral height: short, less than the diam-

eter of the foramen magnum (0); deep, nearly twice the diameter of the

foramen magnum (1) (Wilson, 2002).

7. Parietal contribution to post-temporal fenestra: present (0); absent (1)

(Wilson, 2002).

8. Parietal, distance separating supratemporal fenestrae: less than (0) or

twice (1) the long axis of supratemporal fenestra (Wilson, 2002).

9. Supraoccipital, height: twice (0) subequal to or less than (1) height of fo-

ramen magnum (Wilson, 2002).

10. Paraoccipital process, ventral nonarticular process: absent (0); present (1)

(Wilson, 2002).

11. Tooth shape: spoon-like (0); pencil-like (1) compressed cone chisel-like

(2); pencil-chisel-like (3) (modified from Calvo, 1994).

12. Teeth with wear facets sharply inclined with respect to the labio-lingual

axis: present (0); absent (1) (Salgado and Calvo, 1997).

13. Tooth crowns, cross-sectional shape at mid-crown: D-shaped (0); cylin-

drical (1) (Wilson and Sereno, 1998).

14. Cervical vertebrae, number: 12 (0); 13 (1); 14 or more (2) (Upchurch,

1998).

15. Cervical pleurocoels: absent (0); present (1) (Bonaparte, 1999a,b).

16. Cervical pleurocoels divided by septa (2) (Upchurch, 1998).

17. Cervical prezygapophyses, relative length: long, with articular facets that

surpass the centra (0); short, with articular facets that do not surpass the

centra (1) (Salgado et al., 1997a).

18. High, laminar and laterally expanded cervical neural spines, wider than

the centra: absent (0); present (1) (Gonzalez Riga, 2005).

19. Reduced cervical neural spines with sub-horizontal spinoprezygapophy-

seal laminae: absent (1); present (0) (Gonzalez Riga, 2002).

20. Anterior cervical neural spines, shape: single (0); bifid (1) (Upchurch,

1998).

21. Posterior cervical neural spines, shape: single (0); bifid (1) (McIntosh,

1990).

22. Posterior cervical and anterior dorsal bifid neural spines, median tuber-

cle: absent (0); present (1) (McIntosh, 1990).

23. Cervical vertebrae, general proportions: ratio vertebral height/centrum

length less (0) or more (1) than 1.5. (Calvo and Salgado, 1995).

24. Supradiapophyseal fossa on cervical vertebrae: absent (0); shallow or re-

duced (1); deep and extended (2) (Gonzalez Riga, in press).

25. Middle and posterior cervical centra; anteroposterior length/height of

posterior face: 2.5e3 (0); more than 4.0 (1); less than 2.3 (2) (modified

from Wilson, 2002 by Gonzalez Riga, in press).

26. Centroprezygapophyseal lamina in middle and posterior cervical verte-

brae: single (1); divided (2) (Upchurch, 1998).

27. Dorsal vertebrae, number: 12 (0); 11 (1); 10 or less (3) (McIntosh, 1990).

28. Posterior dorsal centra, articular face shape: amphicoelous (0); opistho-

coelous (1). (Salgado et al., 1997a).

29. Anterior dorsal neural spines, shape: single (0); bifid (1) (McIntosh, 1990).

30. Anterior dorsal neural spines inclined posterodorsally more than 20 de-

gree from vertical: absent (0); present (1) (modified from Wilson and Se-

reno, 1998 by Gonzalez Riga, 2003).

31. Middle and posterior dorsal neural spines, orientation: vertical (0); pos-

terior, with neural spine summit close to the level of diapophyses (1)

(Wilson, 2002).

376 J.F. Bonaparte et al. / Cretaceous Research 27 (2006) 364e376

32. Posterior dorsal neural spines, dorsal development: height of neural spine

(considered from dorsal border of the diapophysis) is more (0) or less (1)

than 25% of the total height of the vertebra (modified from Sanz et al.,

1999 by Gonzalez Riga, 2003).

33. Middle and posterior dorsal neural spines, shape of distal end: tapering or

rectangular (0); lanceolate or transversely expanded (1) (Wilson, 2002).

34. Prespinal lamina in dorsal vertebrae: absent (0); present only as a incipi-

ent prespinal lamina (1); present in the distal end of the neural spine (2);

well developed up to the base of the neural spine (3) (modified from Sal-

gado et al., 1997a).

35. Centroparapophyseal lamina in posterior dorsal vertebrae: absent (0);

present (1) (Bonaparte and Coria, 1993).

36. Ventrally widened or slightly forked centrodiapophyseal laminae in pos-

terior dorsal vertebrae: absent (0); present (1) (Salgado et al., 1997a).

37. Hyposphene-hypantrum articulation in dorsal vertebrae: present (0); ab-

sent (1) (Salgado et al., 1997a).

38. Pleurocoels in dorsal vertebrae, development: lateral cavities devoid of

a sharp border (0); pleurocoels with well-defined borders (1) (Bonaparte,

1999a,b).

39. Pleurocoels in dorsal vertebrae, shape: circular or elliptical (0); posteri-

orly acuminated (eye-shaped) (1) (Bonaparte and Powell, 1980; Salgado

et al., 1997a).

40. Presacral vertebrae with camellate or somphospondylous internal bone

structure: absent (0); present (1) (modified from Wilson and Sereno,

1998, after terminology proposed by Wedel et al., 2000b).

41. Sacral vertebrae, number: less than four (0); four (1); five (2), six (3)

(McIntosh, 1990; Upchurch, 1998).

42. First caudal vertebrae, articular face shape: platycoelous (0); procoelous

(1); opisthocoelous (2); biconvex (3) (Salgado et al., 1997a).

43. Caudal vertebrae, number: more than 45 (0); 35 or fewer (1) (Upchurch,

1998, modified by Wilson, 2002).

44. Caudal transverse processes: disappear by caudal 15 (0); disappear by

caudal 10 (1) (Wilson, 2002).

45. Anterior caudal centra, relative proportions: as high as wide (0); de-

pressed, wider than high (1) (Powell, 2003; Salgado et al., 1997a).

46. Middle and posterior caudal centra: as high as wide (0); depressed, wider

than higher (1) (Powell, 2003; Salgado et al., 1997a).

47. Anterior caudal centra, articular face shape: non-procoelous (0); slightly

procoelous (1); strongly procoelous with prominent condyles (2) (modi-

fied from Salgado et al., 1997a by Gonzalez Riga, 2003).

48. Middle caudal centra, articular face shape: non-procoelous (0); slightly

procoelous (1); strongly procoelous with prominent condyles (2) (modi-

fied from Salgado et al., 1997a by Gonzalez Riga, 2003).

49. Mid point of the neural arch in middle and posterior caudal vertebrae

placed: in the middle of the centrum (0) anteriorly (1) (Huene, 1929; Sal-

gado et al., 1997a).

50. Anterior caudal centra, pleurocoels: absent (0); present (1) (McIntosh,

1990).

51. Anterior and middle caudal centra, ventral longitudinal hollow: absent (0);

present (1) (Upchurch, 1998; Wilson, 2002)

52. Prominent lateral crest on the base of the neural arch in middle caudal

vertebrae: absent (0); present (1) (Salgado et al., 1997a).

53. Anterodorsal border of neural spine in middle caudal vertebrae located

posteriorly with respect to anterior border of the postzygapophyses: pres-

ent (0) absent (1) (Salgado et al., 1997a).

54. Neural spines in the anterior caudal vertebrae, shape: lateromedially

compressed with a long profile in lateral view (0); anteroposteriorly com-

pressed (1) (modified from Wilson, 2002).

55. Neural spines in the middle caudal vertebrae, shape: short anteroposter-

iorly (0); laminated and anteroposteriorly elongated (1) (modified from

Gonzalez Riga, 2003).

56. Prezygapophyses in middle caudal vertebrae, relative length: shorter (0)

or longer (1) than the 40% of the length of the centrum without the pos-

terior articular condyle (Gonzalez Riga, 2003).

57. Ventral depression divided by a longitudinal lamina (septum) on anterior

and middle caudal vertebrae: absent (0); present (1) (Salgado and Azpi-

licueta, 2000).

58. Open haemal canal in anterior caudals: absent (0); present (1) (Upchurch,

1998).

59. Scapular glenoid orientation: relatively flat (0); strongly beveled medially

(1) (Wilson and Sereno, 1998).

60. Humerus, breadth of proximal end: less (0) or more (1) than 50% of total

length (Gonzalez Riga, 2003).

61. Humerus, type of proximal border: strongly curved (0); straight or

slightly curved (1); sigmoidal (2) (modified from Upchurch, 1998 by

Gonzalez Riga, 2002).

62. Ulnar olecranon process, development: prominent, projecting above

proximal articulation (0); rudimentary, level with proximal articulation

(1) (Wilson and Sereno, 1998).

63. Sternal plate, shape: suboval (0); semicircular (1); semilunar (2) (modi-

fied from Salgado et al., 1997a by Gonzalez Riga, 2002).

64. Semilunar sternal plate with straight posterior border: absent (0); present

(1) (Gonzalez Riga, 2003).

65. Coracoid, shape: suboval (0); quadrangular (1) (Salgado et al.,

1997a).

66. Relative metacarpal length: less than 40% of radius length; more than

40% radius length (1) (Salgado et al., 1997a).

67. Metacarpal I, length: shorter (0) or longer (1) than metacarpal IV (Wilson

and Sereno, 1998).

68. Distal phalangeal articular facets on metacarpals: present (0) absent (1)

(Salgado et al., 1997a).

69. Pubis length respect to ischium length: shorter or equal (0); longer (1)

(Salgado et al., 1997a).

70. Ischium, pubic articulation: short (0); long (1) (Salgado et al., 1997a).

71. Ischium, posterior process twice or more the length of pubis articulation:

present (0) absent (1) (modified from Salgado et al., 1997a by Calvo and

Gonzalez Riga, 2003).

72. Ischium, iliac pedicel: short and poor developed (0); slender and well de-

veloped (1); wide and well developed (2) (Calvo and Gonzalez Riga,

2003).

73. Ilium, shape of preacetabular lobe: moderately expanded (0); broadly ex-

panded and dorsally directed (1) (Salgado et al., 1997a).

74. Ilium, orientation of preacetabular lobe: nearly vertical (0); nearly hori-

zontal, laterally projected (1) (Salgado et al., 1997a).

75. Ilium, relative orientation of pubic peduncle: angled (0) or perpendicular

(1) with respect to the sacral axis (Salgado et al., 1997a).

76. Humerus/femoral ratio of 0.90 or more: absent (0); present (1) (McIn-

tosh, 1990).

77. Femur, relative position of the four trochanter: located on the posterior

face, near the midline of the shaft (0); situated on the posteromedial mar-

gin of the shaft (1) (Upchurch, 1998).

78. Lateral bulge of femur below the greater trochanter: absent (0); present

(1) (McIntosh, 1990).

79. Tibia, proportions of distal end: transversal diameter shorter (0) or

greater (1) than anteroposterior diameter (Salgado et al., 1997a).

80. Osteoderms: absent (0); present (1) (Sanz et al., 1999).