A review of the Mesozoic turtles of the Junggar Basin (Xinjiang, Northwest China) and the...

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A review of the Mesozoic turtles of the Junggar Basin(Xinjiang, Northwest China) and the paleobiogeographyof Jurassic to Early Cretaceous Asian testudinates

Márton Rabi & Walter G. Joyce & Oliver Wings

Received: 12 March 2010 /Revised: 10 May 2010 /Accepted: 31 May 2010 /Published online: 2 August 2010# Senckenberg, Gesellschaft für Naturforschung and Springer 2010

Abstract Middle Jurassic to Early Cretaceous sedimentsexposed in the Junggar Basin have yielded a rich turtleassemblage. Jurassic taxa include the purportedly basal turtleSichuanchelys sp. and at least six basal eucryptodires, whichare currently united in the likely paraphyletic taxon“Xinjiangchelyidae.” Early Cretaceous assemblages, bycontrast, include a single “xinjiangchelyid” and a singlepotential pantrionychian, but are otherwise dominated bymore derived eucryptodires, currently grouped in the para-phyletic taxon “Sinemydidae”/“Macrobaenidae.” Compari-son of the Junggar turtle assemblage with those of coeval

Asian localities reveals that Jurassic turtle assemblages wererather homogenous throughout the Jurassic, but split in theEarly Cretaceous. In particular, the Early Cretaceous Junggarturtle assemblage resembles those of other northern Chineseprovinces, Mongolia and the Lake Baikal region of Russia intheir retention of rather basal turtles, whereas all other Asianlocalities are dominated by more derived eucryptodires,particularly pantrionychians. This chasm may be the result ofbiogeographic, ecological and climatic conditions, where dryconditions in isolated inland basins created an ephemerallake habitat optimal for basal eucryptodires, whereas theriver environments typical of the surrounding coastal areaswere favourable for more derived eucryptodires.

Keywords Testudines . Xinjiangchelyidae . Junggar Basin .

Jurassic . Cretaceous

Introduction

Freshwater turtles are generally restricted to their aquatichabitat and may therefore develop patterns of endemism whentheir habitat is fragmented. The development of such endem-isms was particularly favourable in Central Asia for variousaquatic groups of vertebrates throughout the Jurassic (sensuAverianov et al. 2005a; Russell 1993), as the availablelacustrine and fluviatile habitat is thought to have beenrestricted to numerous basins that were separated by mountainbelts (Zhou and Dean 1996) and influenced by differingclimatic conditions (e.g. Eberth et al. 2001). It remainsunclear, however, if these basins were hermetically sealedfrom each other, or if passages along the coasts or within themountain belts allowed for the free exchange of populations.Given that freshwater turtles are among the most commonelements in Central Asian assemblages, a detailed study of

This article is a contribution to the special issue “Triassic–Jurassicbiodiversity, ecosystems, and climate in the Junggar Basin, Xinjiang,Northwest China”

M. Rabi (*)Department of Paleontology, Eötvös Loránd University,Pázmány Péter sétány 1/C,1117 Budapest, Hungarye-mail: [email protected]

W. G. JoyceInstitut für Geowissenschaften, Universität Tübingen,Sigwartstraße 10,72076 Tübingen, Germanye-mail: [email protected]

W. G. JoyceYale Peabody Museum of Natural History,170 Whitney Avenue,New Haven, CT 06511, USA

O. WingsMuseum für Naturkunde Berlin,Leibniz-Institut für Evolutions- und Biodiversitätsforschungan der Humboldt-Universität zu Berlin,Invalidenstraße 43,10115 Berlin, Germanye-mail: [email protected]

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their taxonomy and palaeogeographical distribution isexpected to clarify whether various Central Asian basins wereconnected by lacustrine environments. The Junggar Basin,with its extensive Mesozoic sediment deposits, has a richrecord of fossil freshwater turtles and has thus proven to be akey area in improving our understanding of basal eucrypto-diran evolution and palaeobiogeography. In this review, weprovide a brief overview of the somewhat confusingtaxonomy and publication history of the Mesozoic freshwaterturtles from the Junggar Basin. We also compare the Junggarfauna to other Jurassic to Early Cretaceous faunas of Asia anddiscuss the observed paleobiogeographical pattern.

The earliest scientific finds of fossil turtle material in theJunggar Basin were probably made by a Soviet expeditionworking in the Tukhun-Kho river basin in the years 1941–1942. These materials from the Early Cretaceous TuguluGroup (Hutubin Formation), consisting of shells and imprints,were soon mislaid, but Khosatzky, based on his study of theoriginal drawings and photographs made in the 1950s, nameda new species, ?Sinemys efremovi, in a posthumouslypublished paper (prepared by Nessov and Khosatzky 1996).The original material was recently rediscovered and referredto the genus Wuguia (Danilov and Sukhanov 2006). Furthercontributions to the study of Early Cretaceous turtles fromthe Junggar area were made by Ye (1973), Gaffney and Ye(1992), Brinkman (2001), Maisch et al. (2003), Matzke et al.(2004a, b) and Danilov and Parham (2007), which resulted inthe naming or identification of a total of seven taxa.

In May and June of 1989, the expedition of the Sino–Canadian Dinosaur Project collected several turtle specimensfrom the Late Jurassic Qigu Formation at the Pingfengshan(Wucaiwan) locality in the central Junggar Basin. Thismaterial,corresponding to more than 14 individuals of Xinjiangchelys,was later described by Peng and Brinkman (1993). The Sino–German Project, launched in 1999, concentrated on thesouthern part of the Junggar basin. Fieldwork around the cityof Urumqi revealed several relatively well-preserved turtlespecimens (mostly shells and other postcranial material) in theMiddle Jurassic Toutunhe Formation, the Late Jurassic QiguFormation and the Early Cretaceous Tugulu Group, whichwere subsequently described (Maisch et al. 2003; Matzke andMaisch 2004; Matzke et al. 2004a, b, 2005). In parallel, theexpeditions of an American–Chinese cooperation, led byJames Clark and Xu Xing, has been focusing on the Middleand Late Jurassic assemblages of the central Junggar Basin. Abrief report on their turtle finds was published recently byBrinkman and Matzke (2009).

Geological background

The Junggar Basin is a large continental basin located inXinjiang Uygur Autonomous Region, Northwest China, that

contains an up to 6-km-thick succession ofMesozoic sediments(Dong 1992). Because fossil turtle material has only beenfound in Middle and Late Jurassic and Early Cretaceoussediments, the discussion in this review is mainly restricted toformations within this time interval. All Jurassic andCretaceous strata in the Junggar Basin were deposited in acomplex fluvial–deltaic–lacustrine system. The resulting clas-tic sedimentary sequences can be stratigraphically subdividedinto several, somewhat inconsistently named formations.

Paleobiogeography and sedimentology

During the Early Jurassic, the Junggar District was covered bya large lake in which grey-green and grey-black sandstone andmudstones were deposited (Zhou and Dean 1996). The lakewas surrounded by river drainage systems with shallow-water swamps where coal accumulated along the margins(Zhou and Dean 1996). The complete Junggar–Turpan–Ramiarea was uplifted during the middle Early Jurassic. In theMiddle Jurassic, coinciding with an arid climate, the basinbecame narrower, and shallower; the deposits consist mainlyof purple-red and yellow-green sandstones and mudstones,locally with marlite (Zhou and Dean 1996). This trendcontinued in the early Late Jurassic: the lake became stillshallower and smaller; followed by uplift and denudation.Late Jurassic subsidence resulted in the accumulation of newlacustrine sediment deposits consisting of red to variegatedsandstones and mudstones (Zhou and Dean 1996). The lakepersisted into the early Early Cretaceous (Wang 1988).During this time, the Junggar Lake District was dominatedby lacustrine and, locally, fluvial facies, containing purple-red and grey-green intercalated sandstones, siltstones andmudstones (Zhou and Dean 1996). After uplift and erosionin the middle Cretaceous, a fluvial and locally lacustrinefacies of yellow-brown and purple-red sandstones, conglom-erates and mudstones was deposited in the Late Cretaceous(Zhou and Dean 1996).

Jurassic

The Middle Jurassic Toutunhe Formation in the southernJunggar Basin consists of alluvial plain deposits, mainlymudstones and sandstones. The early Late Jurassic QiguFormation comprises massive red shales and minor sand-stones and also represents alluvial plain sediments. The lateLate Jurassic Kalaza Formation is composed of a planar-bedded conglomerate representing a distal alluvial fan-to-fandelta (Eberth et al. 2001).

In the central and northeastern part of the Junggar Basin,the equivalent formations are the Shishugou Formation, whichnow includes the formerly separate Wucaiwan Formation(Eberth et al. 2001), and the Kalaza Formation. While thelatter is again composed of a conglomerate and megascale,

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cross-bedded sandstone deposited—according to interpreta-tion—as proximal valley fills with alluvial fans, braidedplain and Aeolian dune sediments (Eberth et al. 2001), thesedimentology of the former is more complex. The Shishu-gou Formation is very rich in vertebrate fossils, includingseveral turtle taxa. It mainly consists of sandstones andmudstones that are deposited in an alluvial floodplain and apaludal–lacustrine environment with shallow lakes (Eberth etal. 2001, 2010; Vincent and Allen 2001).

Cretaceous

Early Cretaceous sediments in the Junggar Basin are unitedinto the Tugulu Group and distributed along the northern andsouthern rims of the basin. The Tugulu Group consists of red-green, grey-green and variegated or striped sandy mudstones(Dong 1992), and a large part of this Group consists ofsubaerially deposited sediments and fluvio-lacustrine depositslaid down under semiarid climatic conditions. The TuguluGroup can be divided into four lithological formations, all ofwhich have produced vertebrate fossils (Dong 1992): theQingshuihe Formation, which consists of grey-green sand-stones and basal conglomerates in the lower part and yellow-green or gray-green sandstones alternating with mudstones inthe upper part; the Hutubin Formation (or Hutubihe Fm.;Vincent and Allen 2001), which consists of purple mudstoneswith gray-green siltstones and sandstones, with large scalecross-bedding; the Shengjinkou Formation, comprising gray-green calcareous mudstones and shales; the LianmuqinFormation, which contains red and green variegated mud-stones and arenaceous mudstones, alternating with gray-greensiltstones.

Especially well-preserved vertebrate fossils have beenfound within the Tugulu Group in Urhe (Wuerhe), in thenorthwestern Junggar Basin and in the Dlunshan region(Dong 1992).

Systematic review of Junggar Basin turtles

Jurassic turtles

Testudinata Klein, 1760 sensu Joyce et al. 2004Sichuanchelys Ye and Pi, 1997

Sichuanchelys sp. was recently reported from the LateJurassic Shishugou Formation based on three carapaces(Brinkman and Matzke 2009). The type species,Sichuanchelys chowi, is from the Early Jurassic of Sichuan(Ye and Pi 1997) and characterised by the plesiomorphicretention of mesoplastra. The plastron of the Junggarspecimens are unknown, and their assignment toSichuanchelys was based on the presence of extremelywide rectangular vertebrals (Brinkman and Matzke 2009).

The phylogenetic affinities of Sichuanchelys chowi areunclear, and we consequently do not refer it to a taxonomiccategory more resolved than Testudinata. Danilov andParham (2008) speculated that this taxon may be situatedalong the phylogenetic stem of crown Testudines.

Pancryptodira Joyce, Parham and Gauthier, 2004Eucryptodira Gaffney, 1975 (sensu Gaffney 1984)“Xinjiangchelyidae” Nessov in Kaznyshkin et al. 1990

“Xinjiangchelyids” are medium-sized (carapace length up to375 mm) aquatic turtles known from the Middle Jurassic toEarly Cretaceous of Asia. The monophyly of this assemblagehas never been demonstrated, and the vast majority ofcharacters that are used to diagnose this group (e.g. Sukhanov2000) are symplesiomorphies when mapped onto global trees(e.g. Gaffney et al. 2007; Hirayama et al. 2000; Joyce 2007).As currently circumscribed (e.g. Matzke et al. 2004b),“Xinjiangchelyidae” is therefore likely paraphyletic relativeto “Sinemydidae”/“Macrobaenidae.” The skull, which hasonly been described for Annemys levensis, is characterised bydeep upper and lower temporal emarginations, prefrontals thatcontact one another along the midline and the absence of aninterpterygoid vacuity (Sukhanov 2000). Well-preserved“xinjiangchelyid” skulls from the Late Jurassic Qigu Forma-tion of the nearby Turpan Basin (Wings and Joyce 2009)reveal that the internal carotid arteries entered at the back ofthe skull at the pterygoid/basisphenoid suture, but an openventral groove formed by the basisphenoid reveals that theinternal carotid canal was incompletely floored. We speculatethat the poor preservation of the Annemys levensis type skullobscured this morphology. The shell is low and wide,posteriorly rounded, a nuchal emargination is present, thecarapace has a ligamentous contact with the plastron, theaxillary and inguinal buttresses laterally contact the peripheralsalong grooves, the second to seventh peripherals are thickenedand bent upwards to form a gutter and a pair of reducedepiplastral processes (i.e. cleithra) is present (Sukhanov 2000).

Xinjiangchelyswas erected byYe (1986a) on the basis of acarapace and an incomplete plastron with associated pectoraland pelvic girdles, a distal fragment of a humerus, a femurand a tibia from the late Middle Jurassic or early Late Jurassicof the Jiangjunmiao area in the Junggar Basin. The typespecies, X. junggarensis Ye, 1986a, b, was later synonymisedby Kaznyshkin et al. (1990) with “Plesiochelys” latimargi-nalis Young and Chow, 1953 from Sichuan within the genusXinjiangchelys. Kaznyshkin et al. (1990) furthermore desig-nated X. latimarginalis as the genotype of Xinjiangchelys.Following article 67.1.2. of the International Commission ofZoological Nomenclature (1999), this action is not permissi-ble as “the name of a type species remains unchanged evenwhen it is a junior synonym or homonym, or a suppressedname.” X. junggarensis Ye, 1986a, b, therefore remains thetype species of Xinjiangchelys.

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Xinjiangchelys latimarginalis (Young and Chow 1953)from the Late Jurassic Qigu Formation of the ShishugouGroup [Pingfengshan (Wucaiwan) locality, Junggar Basin] isknown from several shells and other associated postcranialelements that were described by Peng and Brinkman (1993)(Fig. 1a, b). These authors provided a revised diagnosis for X.latimarginalis and supported the synonymy of X. latimargi-nalis and X. junggarensis. However, Peng and Brinkman(1993) noted that the type specimen of X. junggarensis differsfrom all referred specimens of X. latimarginalis by thepresence of a ninth costal, fused first and second peripheralsand a single suprapygal. On the basis of a phylogeneticanalysis of the Xinjiangchelyidae, Matzke et al. (2004b)found that “Plesiochelys” latimarginalis was situated ratherbasal within their “xinjiangchelyid” ingroup separate from X.junggarensis. They consequently excluded X. latimarginalis(sensu Peng and Brinkman 1993) from the genus andconsidered X. junggarensis to be a distinct species. Moreover,Matzke et al. (2004b) differentiated X. latimarginalis sensuKaznyshkin et al. (1990) from X. latimarginalis sensu Pengand Brinkman (1993) and provided a separate diagnosis foreach. Nevertheless, as noted by Danilov and Parham (2008),the data matrix of Matzke et al. (2004b) lacks appropriateoutgroup taxa, and their conclusions are thus questionable.

While X. junggarensis shows a distinct morphology and maypotentially represent a valid species, “Plesiochelys” latimar-ginalis and the two morphotypes of X. latimarginalis ofMatzke et al. (2004b) are distinguishable by characters thatare very likely to be subject of individual variation. However,only a relatively large sample of specimens combined with aglobal phylogenetic analysis could clarify the validity ofthese taxa. Undescribed material belonging to an extremelylarge number of individuals from the Turpan Basin of Chinacould potentially contribute to our understanding of morpho-logical variation in “xinjiangchelyids” (Wings and Joyce2009).

The main characteristics of X. latimarginalis include acarapace length up to 360 mm, a smooth shell surface, ashallow and wide nuchal emargination, an anteroposteriorlyelongated first peripheral, presence of a contact between thefirst suprapygal and the tenth peripheral and a wide,rectangular anterior plastral lobe (Matzke et al. 2004b;Peng and Brinkman 1993).

Xinjiangchelys sp. A (sensu Peng and Brinkman 1993)has been reported from the same Pingfengshan (Wucaiwan)locality that yielded several specimens of X. latimarginalis.It is distinct from the latter in its elongated plastral lobesand narrower bridge area. However, it is represented only

Fig. 1 Examples of fossil turtles recovered from Jurassic sediments in theJunggar Basin, Xinjiang Autonomous Uygur Region. Xinjiangchelyslatimarginalis (Young and Chow 1953): a carapace and b plastronredrawn from Peng and Brinkman (1993). Xinjiangchelys qiguensisMatzke et al., 2004b: c carapace and d plastron redrawn from Matzke et

al. (2004b). Annemys levensis Sukhanov and Narmandakh 2006, basedon material found in Mongolia: e carapace and f plastron redrawn fromSukhanov (2000). Annemys sp., based on a previously unpublished skullmentioned by Brinkman and Matzke (2009) from the Junggar Basin: gdorsal view and h ventral view. Specimens not drawn to scale


by one specimen consisting of a plastron and partialcarapace, and Peng and Brinkman (1993) therefore felt thatthe material is inadequate for the erection of a new taxon.Matzke et al. (2004b) noted that the carapace fragmentoriginates from the middle portion of the carapace and notthe posterior part. The alleged presence of a ninth costaland ninth neural is therefore not supported by the availablematerial, and Xinjiangchelys sp. becomes more similar toother Xinjiangchelys species, in particular to Xinjiangchelysqiguensis (Matzke et al. 2004b).

Xinjiangchelys chowi Matzke et al., 2005 was describedfrom the Middle Jurassic (Callovian) Toutunhe Formationnear the city of Urumqi at the southern margin of theJunggar Basin. This species is based on a single partialshell, including an almost complete carapace and the righthypoplastron (carapace length: 345 mm). According toMatzke et al. (2005), the two anterolateral carapacialperipheral fontanelles, a thin plastron with large lateralfontanelles and a median hypoplastral suture with strongpegs are autapomorphies of X. chowi. Although all of thesecharacters could be interpreted as juvenile traits, Matzke etal. (2005) discounted the possibility that the type specimenis a juvenile because it is among the largest known“xinjiangchelyids.” Again, undescribed material from theTurpan Basin belonging to a large number of individualsand preliminarily referred to X. cf. chowi may clarifythe validity of this species (Wings and Joyce 2009). Thepresence of fontanelles in the carapace and pegs in theplastron were interpreted by Matzke et al. (2005) as derivedfeatures within the genus, and X. chowi therefore appears tobe the most advanced species of Xinjiangchelys. Given thatthis taxon is also one of the oldest “xinjiangchelyids,”extensive ghost ranges are predicted for all other “xinjiang-chelyid” lineages. However, the exact stratigraphic positionof Xinjiangchelys chowi is unclear, and an early LateJurassic age is possible.

Xinjiangchelys qiguensis Matzke et al., 2004b originatedfrom the same region as X. chowi but from the lowermostpart of the overlying Qigu Formation (Late Jurassic,Oxfordian, Fig. 1c, d). This taxon is therefore contempo-raneous with several specimens of X. latimarginalis thatwere described by Peng and Brinkman (1993, see above)from the Shishugou Formation in the Northern JunggarBasin. The type and only specimen consists of a shell(carapace length: 375 mm) and a number of associatedpostcranial elements, including the scapulae, pelvis, ulnaand nearly all cervical vertebrae. Among others, X.qiguensis is distinguished from other Xinjiangchelys bythe extension of the first and fifth vertebrals onto theperipherals, three pairs of gulars and an intergular that doesnot contact the hyoplastron. In addition, the shoulder girdleis unique in the presence of a long acromial process butshort scapular processes, the pelvis has a posterior iliac

process that is longer than the iliac shaft and the cervicalsare elongated.

According to the phylogenetic analysis of Matzke et al.(2004b), X. qiguensis is the most basal representative ofXinjiangchelys and more derived than “P.” latimarginalis.Plesiomorphic traits include the fifth vertebral extendingstrongly onto the peripherals, anteriorly directed axillaryprocesses, gular scutes that do not extend onto thehyoplastron, and pectoral scutes that are much smaller thanthe abdominal scutes.

Xinjiangchelys radiplicatus (Young and Chow 1953) is asmall turtle (maximum carapace length: 250 mm) based ontwo shells from Sichuan (Ye 1986b; Young and Chow 1953)that were originally described as Plesiochelys radiplicatus, butlater referred to Xinjiangchelys by Kaznyshkin et al. (1990)and Peng and Brinkman (1993). The first specimens from theJunggar Basin were reported by Maisch et al. (2003) whoreferred an incomplete carapace and plastron together withother pieces of a small decorated turtle to X. cf. radiplicatusfrom the upper Toutunhe Formation (Middle Jurassic) atLiuhuanggou. Matzke et al. (2004b) later suggested that thepresence of small peripheral fontanelles, a small size and thedistinct sculpture of the shell might be juvenile features andthat the material may represent an already recognised species.Brinkman and Matzke (2009) recently identified a skull withassociated shell and other isolated plates as cf. X. radiplicatus(misspelled as “radiplicus”) from the Shishugou Formation.Thus, the number of decorated turtle specimens is increasing,and further studies may confirm the validity of this taxon. Theskull reported by Brinkman and Matzke (2009) showsshallow temporal and cheek emargination and a triangularbasisphenoid similar to that of Chubutemys copelloi fromArgentina (Gaffney et al. 2007). The shell of X. radiplicatus isdecorated with radially oriented ridges and grooves that areindependent from the bony pattern but associated with thesulci (Matzke et al. 2004b).

Annemys sp. Sukhanov and Narmandakh 2006 is anotherturtle taxon from the Junggar Basin that has been reported asa skull–shell association (Brinkman and Matzke 2009), but aformal description is still outstanding (Fig. 1e–h). Thispossible “xinjiangchelyid” genus was established on thebasis of a partial shell from the Late Jurassic of Sharteg,Mongolia and includes two species, A. latiens and the A.levensis, the latter of which is based on a skull–shellassociation (Sukhanov and Narmandakh 2006). Matzke etal. (2004b) considered Annemys latiens to be a juniorsynonym of Xinjiangchelys based on a phylogenetic analysisof the “Xinjiangchelyidae.” All known skulls of Annemyspossess deep temporal and cheek emarginations, as in thepartial skull from the Callovian of Kyrgyzstan referred to X.latimarginalis (Kaznyshkin et al. 1990), unlike cf. Xin-jiangchelys radiplicatus and Xinjiangchelys cf. chowi, thefew other “xinjiangchelyids” for which a skull is known


(Brinkman and Matzke 2009; Danilov et al. 2005; Sukhanov2000; Sukhanov and Narmandakh 2006; Wings and Joyce2009). Together with the presence of a large foramenpalatinum posterius and the narrow vertebrals, Annemysspp. are more similar to the “macrobaenid” Hangaiemys spp.from the Early Cretaceous of Mongolia than to Xin-jiangchelys (Brinkman and Matzke 2009), thus supportingthe possible paraphyly of the “Xinjiangchelyidae” ascurrently constructed.

Early Cretaceous turtles

“Xinjiangchelyidae” Nessov, in Kaznyshkin et al. 1990

Xinjiangchelys sp. B (sensu Danilov and Parham 2007)from the Early Cretaceous (Aptian–?Albian) upper TuguluGroup (Wuerho locality) in the southern Junggar Basin isone of the latest records of “Xinjiangchelyidae,” consider-ably extending the temporal range of this group from theMiddle–Late Jurassic to the Early Cretaceous. The onlyshell of this turtle (carapace length: 230 mm) is theholotype of the problematic taxon “Sinemys” wuerhoensis(Ye 1973), which was erected on the basis of a series ofshells and skulls on three slabs of limestone recentlyrevealed to be a chimera (Danilov and Parham 2007, seebelow). Currently, “S.” wuerhoensis is recognised as anomen dubium since the type specimen does not show anyautapomorphies and greatly resembles X. latimarginalissensu Peng and Brinkman, 1993 (Danilov and Parham2007). Although X. sp. B differs from X. latimarginalis inits plastral proportions and the presence of a centralfontanelle variation in Xinjiangchelys is too poorly known,the specific assignment of the Wuerho specimen iscurrently unclear.

“Sinemydidae” Ye, 1963“Macrobaenidae” Sukhanov, 1964

Most Early Cretaceous eucryptodiran turtles more derivedthan “xinjiangchelyids” are often referred to “sinemydids” and/or “macrobaenids”. However, the monophyly of these twogroups is doubtful, and their taxonomical composition istherefore controversial (Brinkman 2001; Brinkman and Peng1993a, b; Gaffney 1996; Gaffney et al. 2007; Gaffney and Ye1992; Joyce 2007; Parham and Hutchison 2003). We hereinpartly follow Gaffney et al. (2007) by collectively referring tothese turtles as “Sinemydidae”/“Macrobaenidae.” Our usageof this term is nevertheless more restrictive than that ofGaffney et al. (2007), as we only include turtles formerlyclassified as Sinemydidae and Macrobaenidae and not“xinjiangchelyids” and meiolaniids. Two main skull mor-phologies are apparent within this group. Sinemys lens ischaracterised by extremely deep, confluent upper temporaland cheek emarginations due to the lack of a temporal bar,prefrontals that do not meet one another along in the midline,

an elongated basisphenoid and an enclosed incisura columellaauris (Brinkman and Peng 1993a). On the other hand,Ordosemys spp., Dracochelys bicuspis and Kirgizemys spp.possess only a moderate upper temporal emargination, butdeep cheek emarginations, medially meeting prefrontals, anopen incisura columellae auris and a short basisphenoid(Brinkman and Peng 1993a; Danilov et al. 2006; Gaffney andYe 1992; Sukhanov 2000; Tong et al. 2004). The shell ofSinemys spp. is highly aberrant: the pygal bone is absent, thetwelfth peripherals are reduced, a ninth neural is present andthe seventh peripherals are developed into laterally protrudingspines (Brinkman and Peng 1993a).

Wuguia hutubeiensis Matzke et al. 2004a is a recentlydescribed “sinemydid”/“macrobaenid” turtle from the EarlyCretaceous (Hauterivian–Barremian) Hutubei Formation(Tugulu Group) of the southwestern Junggar Basin (Haojia-gou section, Fig. 2a). It is known from several almostcomplete and partial shells (carapace length: 137 mm), anisolated scapula, and an ilium. Wuguia hutubeiensis isdiagnosed from other “sinemydids”/“macrobaenids” by aunique combination of traits, including the absence of anuchal emargination and carapacial fontanelles, at least twosuprapygals, presence of a cervical scute, a ligamentousconnection of the plastron and the carapace, absence oflateral and central plastral fontanelles and an elongatedposterior plastral lobe. A remarkable feature of this species isthe high degree of individual variation within the nuchal andsuprapygal regions: additional ossifications and unique bonearrangements are apparent and independent of ontogeny orsexual dimorphism. Matzke et al. (2004b) suggested that W.hutubeiensis was characterised by a genetic predispositionfor unusually strong variation in the anterior and posteriorsegments of the carapace. Not unexpectedly, the variationsoccur with the nuchal, first peripheral and suprapygal, all ofwhich have been demonstrated by Zangerl (1969) to possessmore variability, perhaps because they are not closelyassociated with the axial skeleton.

Wuguia efremovi (Khosatzky 1996) originates from theHutubei Formation, just as W. hutubeiensis (Fig. 2b). Thetype and only known specimen consists of the imprints andsteinkern of a complete and a partial shell collected in 1941–1942, originally referred to ?Sinemys efremovi by Khosatzky(1996) in his posthumously published paper. The specimenswere misplaced until recently, and so Khosatzky (1996)described this taxon based on photographs and drawingsfrom the 1950s. Brinkman (2001) later excluded ?S. efremovifrom the genus Sinemys (Wiman 1930) but did not attempt toclarify its taxonomic position. Danilov and Sukhanov (2006)recently rediscovered the type material and referred “S.”efremovi to the genus Wuguia. They based this assignmenton the absence of a nuchal emargination, additionalossifications in the suprapygal, extension of the 12thmarginals onto the second suprapygal, elongated posterior


lobe of the plastron and the similar size (carapacial length:150 mm). However, they maintained the validity of bothspecies, as W. efremovi can be distinguished from W.hutubeiensis on the presence of carapacial and plastralfontanelles, a midline contact of the eighth costals and thethird vertebral being wider than long and wider than thefourth and fifth vertebrals. Danilov and Sukhanov (2006)further synonymised Dracochelys wimani (Maisch et al.2003), a shell-based taxon from the Lianmuxin Formation(Wuerho district) of the Tugulu group, with W. efremovi.

Dracochelys bicuspis Gaffney and Ye 1992 from theLianmuxin Formation (Wuerho district) is based on a single,well-preserved cranium (Fig. 2f), which was originallyfigured and identified as an “amphichelydian” by Ye(1973). Although Gaffney and Ye (1992) did not undertakea formal phylogenetic analysis, they nevertheless notedsimilarities with Hangaiemys hoburensis, a “sinemydid”/”macrobaenid” turtle from the Early Cretaceous of Mongo-lia. Brinkman (2001) referred a partial skeleton to D.bicuspis (Fig. 2e) based on the presence of a symphysealhook, narrow triturating surface, and the size of the lowerjaw, but given that the skeleton lacks the cranium, thisassignment has to be viewed with caution. D. bicuspis has aflattened skull, narrow triturating surfaces, large foraminapalatinum posterius, large internal nares, and a ninth neural,which is crossed by the sulcus between the fourth and fifthvertebrals. All of these traits are shared with Hangaiemyshoburensis. An autapomorphic character of D. bicuspis is thepresence of a tooth-like process on the lateral surface of the

premaxilla–maxilla suture. With its 45-mm-long skull, thisspecies is the largest among the Tugulu group turtles. Asmentioned by Gaffney and Ye (1992), the proportions andshape of the skull and the narrow, hooked beak are stronglyreminiscent of the extant North American snapping turtleChelydra serpentina, and D. bicuspis possibly occupied asimilar ecological niche as recent snapping turtles do.

The majority of specimens that comprise the type series of“S. wuerhoensis” (see above) are now referred to Ordosemysbrinkmania Danilov and Parham, 2007 (Fig. 2c, d). Thistaxon is represented by a number of skulls and shells, someof which are in association. Although the skulls aredeformed, and sutures are not very well preserved, theyshare with other species of Ordosemys the absence of amedian prefrontal contact as a result of a long anteriorprocess of the frontals. Furthermore, the shell (carapacelength: 153–215 mm) possesses a preneural bone and threesuprapygals. Ordosemys brinkmania differs from otherspecies of this genus in the deeper temporal emargination,the anterior projection of the first vertebral, and the absenceof a hypo–xiphiplastral fontanelle. Ordosemys is a diverseand widespread genus in the Early Cretaceous of China andMongolia, but only O. brinkmania has been reported fromthe Junggar Basin.

Pantrionychia Joyce, Parham and Gauthier, 2004

cf. Pantrionychia indet. is the third taxon that forms partof the original type series of “S. wuerhoensis” (Danilov andParham 2007). It is based on a single, poorly preserved

Fig. 2 Examples of fossil turtlesrecovered from Cretaceoussediments in the Junggar Basin,Xinjiang Autonomous UygurRegion. Wuguia hutubeiensisMatzke et al. 2004a: a carapaceredrawn from Matzke et al.(2004a). Wuguia efremovi(Khosatzky 1996): b carapaceredrawn from Maisch et al.(2003). Ordosemys brinkmaniaDanilov and Parham, 2007:c carapace and d plastronredrawn from Danilov andParham (2007). Dracochelysbicuspis Gaffney and Ye, 1992: ecarapace redrawn from Brinkman(2001), f skull redrawn fromGaffney and Ye (1992).Specimens not drawn to scale


skull only visible in dorsal aspect. Only the parietal–parietaland the parietal–supraoccipital sutures are visible, and mostof the left side of the skull is eroded. This specimen ischaracterised by deep temporal emarginations, short post-orbitals and dorsally oriented orbits, and is thereforestrongly reminiscent to extant trionychians.

Relationships of Junggar Basin turtles

The basalmost turtle of the Junggar Basin is likelySichuanchelys (Brinkman and Matzke 2009), which hasbeen argued to be a stem-testudine by Danilov and Parham(2008), possibly close to Kayentachelys aprix.

The interpretation of “Xinjiangchelyidae” as basal eucryp-todires is widely accepted in the literature, and most authorsconsider this clade to be more closely related to moderncryptodires than Paracryptodira or Plesiochelyidae (Gaffney1996; Hirayama et al. 2000; Joyce 2007; Parham andHutchison 2003) and, with the exception of Danilov andParham (2008), basal to “Sinemydidae”/“Macrobaenidae”.Hirayama et al. (2000) concluded that the European taxonBrodichelys brodei may be a close relative of “Xinjiangche-lyidae,” whereas Danilov and Parham (2008) noted closerelationships with Asian Chengyuchelys spp. As it stands, allglobal analyses hand pick a select number of one or two“xinjiangchelyids” (e.g. Danilov and Parham 2008; Gaffney1996; Hirayama et al. 2000; Joyce 2007; Parham andHutchison 2003), and all “xinjiangchelyid” analyses arehighly limited in their taxon sample (e.g. Matzke et al.2004b; Peng and Brinkman 1993). Finally, the vast majorityof characters typically listed as diagnostic for the grouprepresent symplesiomorphies for Eucryptodira (e.g. Danilovand Parham 2008; Gaffney 1996; Hirayama et al. 2000;Joyce 2007; Parham and Hutchison 2003). It is thereforehighly plausible that “Xinjiangchelyidae” as currently con-structed is paraphyletic.

Most Early Cretaceous turtles from the Junggar Basin arereferable to “Sinemydidae” and/or ”Macrobaenidae,” a para-phyletic assemblage of basal eucryptodiran turtles morederived than “xinjiangchelyids” and typically resolved as thesuccessive sister taxa of Polycryptodira (sensu Gaffney 1996)or crown Cryptodira (Joyce et al. 2004). These forms aregenerally known from the Cretaceous and Paleogene of Asiaand North America (Brinkman 2001; Brinkman and Peng1993a; Gaffney and Ye 1992; Parham and Hutchison 2003;Sukhanov 2000). The paraphyly of “sinemydids” marcobae-nids” has been recently confirmed by the phylogeneticanalyses of Gaffney et al. (2007) and Joyce (2007). Amongothers, the topology of Gaffney et al. (2007) differs from thatof Joyce (2007) in that Ordosemys leios is not sister toSinemys lens and primitive to Dracochelys bicuspis. Ascurrently understood, the closest relatives of the Junggar

“sinemydids”/“macrobaenids” come from the Jurassic–Creta-ceous of Mongolia, China, Russia and Kyrgyzstan (Brinkmanand Peng 1993a; Danilov et al. 2006; Nessov and Khosatzky1973, 1981). The fact that “Xinjiangchelyidae, “Sinemydi-dae” and “Macrobaenidae” form successively internestedparaphyletic groups, coupled with the fact that the vastmajority of taxa attributable to these grades are Asian,strongly confirms the notion that the stem evolution of crownCryptodira occurred in Asia.

Palaeobiogeography

The Middle to Late Jurassic turtle assemblages of theJunggar Basin almost exclusively consist of “xinjiang-chelyids”, with the exception of Sichuanchelys sp., apossible stem-testudine. This composition is comparableto other Asian assemblages, including the adjacent TurpanBasin in Xinjiang (Xinjiangchelys cf. chowi, Annemys cf.latiens), Sichuan (Xinjiangchelys spp., Chengyuchelysspp.), Mongolia (Annemys spp., Shartegemys laticentra-lis, Undjulemys platensis), Russia (Xinjiangchelys sp.),Thailand (Siamochelys peninsularis) and Kyrgyzstan(Xinjiangchelys spp.), where “xinjiangchelyids” are thedominant, or in most cases, the sole elements of theassemblage (Danilov et al. 2005; Danilov and Parham 2008;Kaznyshkin 1988; Kaznyshkin et al. 1990; Sukhanov 2000;Sukhanov and Narmandakh 2006; Tong et al. 2002; Wingsand Joyce 2009; Ye 1963, 1986b; Young and Chow 1953).Within the Jurassic, more derived eucryptodires are onlyknown from Shandong (Sinemys lens) and Sichuan (thepantrionychid Yehguia tatsuensis and Sinaspiderites wimani)(Brinkman and Peng 1993a; Danilov and Parham 2006;Young and Chow 1953). As currently understood, theJunggar Basin has produced the most diverse Jurassic turtleassemblage in Asia, and a number of endemisms areapparent at the species level (Table 1).

The late Early Cretaceous (Barremian–Aptian) turtleassemblages of the Junggar Basin almost exclusively consistof basal eucryptodires, predominately “sinemydids” and/or“macrobaenids”. Other approximately coeval localities ofChina show the same taxonomic distribution: the Barremian–Aptian Yixian Formation yielded remains of Ordosemysliaoxiensis and Manchurochelys manchoukuoensis, the Hau-terivian–Albian Luohandong Formation yielded Sinemysgamera and Ordosemys leios and the assemblage from theBarremian–Aptian Xinminbao Group is characterised by the“sinemydid”/“macrobaenid” Kirgizemys kansuensis (Bohlin1953; Brinkman and Peng 1993a, b; Sukhanov 2000; Tonget al. 2004; Table 2, Fig. 3). Sinochelyids, a possibly basalgroup of turtles not closely related with Eucryptodira(Hirayama et al. 2000), are known from the Aptian ofShandong and the Albian of Gansu (Peishanemys laptions


Tab

le1

Tem

poralandgeog

raph

icdistribu

tionof

Jurassic

turtle

faun

asof

Asia

Num

berscorrespond

toreferences

1Brinkman

andMatzke(2009);2Ye(1986a);

3Matzkeet

al.(2004b),

4Peng

andBrinkman

(1993);5Matzkeet

al.(2005);6Maischet

al.(2003);7Wings

andJoyce(2009);

8Young

andChow(1953);8

*Young

andChow(1953),Y

e(1986b);

9Ye(1999);10Ye(1963),D

anilo

vandParham

(2008);1

1Young

andChow(1953),D

anilo

vandParham

(2008);12Ye(1994);1

3Wim

an(1930),

Peng

andBrinkman

(1993),S

ukhanov(2000);1

4Su

khanov

(2000),S

ukhanovandNarmandakh

(2006);1

5Danilo

vetal.(2005);

16To

ngetal.(2009a);1

7To

ngetal.(2002);

18Kaznyshkin(1988);K

aznyshkinetal.

(1990);19cf.Sh

achemydinae

sensuNessov(1984),Xinjia

ngchelys

sp.accordingto

Igor

Danilo

v(personalcommunication)

Alltaxa

arebasaleucryp

todires(“xinjiang

chelyids”and“sinem

ydid”/“m

acrobaenids”)except

where

noted

ST:Stem-Testudines;SI:Sinochelyidae;PT:Pantriony

chia

Notethat

basaleucryp

todiresarewidespreadthroug

halargepartof

Asiadu

ring

theMiddleandLateJurassic


Tab

le2

Tem

poralandgeog

raph

icdistribu

tionof

Early

Cretaceou

sturtle

faun

asof

China

andMon

golia

(paleogeog

raph

ically

inland

areas)

Num

bers

correspo

ndto

references

1Danilo

vandParham

(200

7);2Gaffney

andYe(199

2),Brinkman

(200

1);3Maischet

al.(200

3),Danilo

vandSukhano

v(200

6);4Matzkeet

al.(200

4a),Matzkeand

Maisch(200

4);5Kho

satzky

(199

6),D

anilo

vandSuk

hanov(200

6);6Boh

lin(195

3),D

anilo

vetal.(20

06);

7Ye(196

5),D

anilo

vandVitek(200

9);8Brinkman

andPeng(199

3a);

9Brink

man

andPeng(199

3b),

Brinkman

andWu(199

9);10To

nget

al.(200

4);11End

oandShikama(194

2),Sukhano

v(200

0);12Chow

(195

4);13Danilo

vandSyrom

yatnikov

a(200

8);14Nessov(198

1);15SukhanovandNarmandakh

(197

4),Sukhano

v(200

0),Danilo

vet

al.(200

6);16ShuvalovandChk

hikvadze

(197

9),Sukhano

v20

00,Danilo

vet

al.20

06;17Khand

etal.(200

0),Suk

hanov(200

0),Suk

hanovandNarmandakh

(197

4);

18Sukhano

v(200

0),SukhanovandNarmandakh

(200

6),Danilo

vet

al.(200

6);19Sukhano

v(200

0),Sukhano

vandNarmandakh

(200

6),Danilo

vandParham

(200

7);20Kho

satzky

(199

9)

Alltaxa

arebasaleucryp

todires(“xinjiang

chelyd

s”and“sinem

ydid”/”m

acrobaenids”)except

where

noted

SI:Sinochelyidae;PT:Pantriony

chia;PTE:Pantestud

inoidea

Notethat

thepaleog

eographically

inland

areasaredo

minated

bybasaleucryp

todiranturtles


Bohlin, 1953; Chow 1954; Sukhanov 2000). On the otherhand, pantrionychians are very rare, known only from theJunggar Basin (cf. Pantrionychia indet. sensu Danilov andParham, 2007) and Inner Mongolia (“Aspideretes” spp.;Danilov and Vitek 2009; Ye 1965). Early Cretaceouspantestudionids have only been reported from the Aptian ofMongolia (Mongolemys sp.; Khand et al. 2000; Sukhanov2000; Sukhanov and Narmandakh 1974). Basal eucrypto-dires and sinochelyids are also dominant elements in theEarly Cretaceous of Mongolia, including Sinochelys spp.,Peishanemys testudiformis, Kirgizemys hoburensis (= Hang-aiemys hoburensis according to Danilov et al. 2006), K. leptisand Ordosemys perforata (= Asiachelys perforata accordingto Danilov and Parham 2007), ranging from the Aptian tothe Albian (Sukhanov and Narmandakh 1974; Shuvalovand Chkhikvadze 1979; Sukhanov 2000; Sukhanov andNarmandakh 2006). Kirgizemys is also well known fromBarremian to Albian deposits in the Lake Baikal region ofRussia (Danilov et al. 2006; Nessov and Khosatzky 1981).The Early Cretaceous Junggar assemblage is considered tobe partly endemic, even at the generic level, given that onlyOrdosemys and Xinjiangchelys have been hitherto reportedoutside of the basin (Tables 2 and 3, Fig. 3).

Contrary to China, Mongolia and the Lake Baikal regionof Russia, other late Early Cretaceous Asian turtle

assemblages, including those of Japan, Laos, Thailand andKyrgyzstan were characterised by adocid and nanhsiung-chelyid trionychians and, perhaps questionably, by stem-testudinoids during the Barremian–Albian, with a very fewbasal eucryptodires such as Kirgizemys exaratus (Danilovand Parham 2007; de Lapparent de Broin 2004; Hirayamaet al. 2000; Tong et al. 2009b; Tables 2 and 3, Fig. 3).

Interrelated geographic, ecological and climatic factorsshould be taken into account for possible explanations ofthis distributional pattern. During the Early Cretaceous,northern China, Mongolia and the Lake Baikal region ofRussia were inland areas, while Japan, Laos and Thailandrepresented the eastern and Kyrgyzstan the western coastalregion (Fig. 3). It is therefore possible that the descendentsof formerly widespread basal eucryptodiran stock wereisolated during the Early Cretaceous in these inland areasand retained their relatively conservative morphology andhabitat preferences until the late Early Cretaceous.

In terms of the depositional environment, those Jurassic–Early Cretaceous strata ofAsia whichwere dominated by basaleucryptodiran turtles (corresponding to almost exclusivelyinland areas) were dominantly characterised by extensivelacustrine sedimentation (Averianov et al. 2003, 2005a, b;Bohlin 1953; Dong 1992; Eberth et al. 2001; Jerzykiewicz2000; Khand et al. 2000; Khosatzky 1996; Lee et al. 2009;

Fig. 3 Paleobiogeography ofturtles during the Early Cretaceousin Asia. From Shandong (China),Övörkhangai (Mongolia) andSouth Korea only one taxon hasbeen described (Peishanemys lap-tions, Nanhsiungchelydae indet.and Kirgizemys cf. K. exaratus,respectively). Black areas are la-custrine facies, grey areas arefluvial and/or coastal facies. Notethat the distribution and domi-nance of basal eucryptodires arelinked to lacustrine environmentswhich, with the exception ofSouth Korea, were typical for thearid-semiarid inland areas. Pan-trionychians, on the other hand,dominated the fluvial environ-ments along the coastal areas.This pattern is not apparent for theJurassic when lacustrine habitatswere also present close to thecoasts (in Thailand and Kyrgyz-stan), and basal eucryptodireswere the most diverse and abun-dant turtles of Asia. Base map(120 Ma, Aptian) courtesy of RonBlakey. For references on distri-bution, see caption of Table 2


Tab

le3

Tem

poralandgeog

raph

icdistribu

tionof

Early

Cretaceou

sturtle

faun

asof

Russia,

Thailand

,Laos,

Sou

thKorea,JapanandKyrgy

zstan(paleogeog

raphically

coastalareaswith

the

exceptionof

Russia)

Num

berscorrespond

toreferences

1NessovandKhosatzky

(1981),Danilovet

al.(2006);2Danilo

vet

al.(2006);3To

nget

al.(2005),(2009b);

4To

nget

al.(2009b);

5To

nget

al.(2006),(2009b);

6To

nget

al.

(2009b);

7Lapparent

deBroin

(2004);8

Lee

etal.(2009);

9Hirayam

a(2002);9

*Hirayam

a(2002),D

anilo

vandSy

romyatnikova(2008);1

0So

noda

andHirayam

a(2009);1

1NessovandKhosatzky

(1973);1

2Nessov

andKhosatzky

(1977);13Nessov(1995)

Alltaxa

belong

topantrion

ychiansexcept

where

noted

BE:basaleucryp

todire

Notethat

thepaleog

eographically

coastalareasaredo

minated

bypantrion

ychian

turtles


Sinithsenkova 2002; Sukhanov and Narmandakh 1974;Swisher et al. 1999; Tong et al. 2002; Wings and Joyce2009; Fig. 3). On the other hand, the coastal environmentsdominated by pantrionychians were characterised by fluvialsedimentation (Hirayama et al. 2000; Hirayama 2002; Isaji etal. 2006; Lapparent de Broin 2004; Tong et al. 2002, 2006,2009a, b; Fig. 3). Similar to their extant descendents,pantrionychians were likely excellent swimmers and betteradapted to high-energy riverine conditions. By contrast, itappears that the more generalised basal eucryptodirespreferred low-energy lakes and swamps. In accordance withthis, Peng and Brinkman (1993) noted that the lacustrinefacies of the Late Jurassic Qigu Formation at Pingfengshan(Wucaiwan) contrasts with the coeval fluvial facies ofJiangjunmiao (100 km to the east) in the complete dominanceof turtle remains in the former. The presence of Dracochelysbicuspis, a possible ecomorphological equivalent to theRecent North American snapping turtle Chelydra serpen-tina (Gaffney and Ye 1992), in the former lake of theJunggar Basin is also consistent with this hypothesis. Thediscovery of Kirgizemys cf. K. exaratus in the high-latitude Lower Cretaceous lacustrine facies of SouthKorea (Lee et al. 2009) confirms that the distribution ofbasal eucryptodires was more linked to paleoenvironmentthan to paleogeography (Fig. 3).

Finally, climatic conditions likely also influenced thisbiogeographical pattern as the seasonally arid climate in theinland areas favoured the development of semi-permanentlakes, while the humid climate in the coasts favoured theformation of large river systems.

Summary

The high diversity of taxa, the favourable taphonomicconditions, and the long time span ranging from the MiddleJurassic to the Early Cretaceous make the Junggar Basin a keyarea in our understanding of basal eucryptodiran relationshipsand provide insight into a particularly important period ofcryptodiran evolution. The extreme longevity of this exten-sive, partly isolated, lake-dominated basin provides an idealopportunity to study palaeobiogeography and endemisms ofMesozoic turtles in Asia. As currently known, the JunggarBasin yields the most diverse pre-Late Cretaceous turtleassemblages in Asia and, contrary to the regionally extensiverecord of Mongolia, the turtle assemblage is derived from aconsiderably small area.

The composition and the relict nature of the Junggarturtle assemblage as well as other inland turtle assemblagesmay indirectly infer, together with sedimentological evi-dence, that the origin of basal eucryptodires primarily tookplace in lacustrine environments. Based on their distribu-tion pattern, basal eucryptodires presumably also never

became dominant elements in subsequent fluvial habitats.Although the skeletal anatomy of most basal eucryptodiresconfirms this assertion, there are some exceptions. Forinstance, the relatively large size of Anatolemys spp.probably allowed them to inhabit fluvial and estuarineenvironments (Nessov 1985, 1987), while Sinemys gameraand S. lens from the Ordos Basin developed a pair ofposterolaterally directed carapacial spines that may havehad a hydrodynamically stabilising function in higherenergy environments (Brinkman and Peng 1993a).

Although the turtles from the Junggar Basin have beenstudied for more than 70 years, with increased intensity inthe last 20 years, much work is yet to be done. Furtherclarification of the phylogenetic relationships, intraspecificvariation, paleocology and paleobiogeography are expectedto be rewarding tasks for future researchers.

Acknowledgements We would like to thank Don Brinkman, IgorDanilov and Thomas Martin for thoughtful comments and discussionsthat helped improve the quality of this manuscript. Don Brinkman isfurthermore thanked for providing us with photographs and linedrawings of an unpublished Annemys skull from the Junggar Basin,which served as the basis of our line drawing presented in Fig. 1g, h.

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