ARTICLE

A NEW MIDDLE TRIASSIC EOSAUROPTERYGIAN (REPTILIA, SAUROPTERYGIA) FROMSOUTHWESTERN CHINA

DA-YONG JIANG,*,1 OLIVIER RIEPPEL,2 RYOSUKE MOTANI,3 WEI-CHENG HAO,1 YUAN-LIN SUN,1

LARS SCHMITZ,3 and ZUO-YU SUN1

1Department of Geology and Geological Museum, Peking University, Beijing 100871, P.R. China, djiang@pku.edu.cn;2Department of Geology, The Field Museum, Chicago, Illinois 60605-2496, U.S.A.

3Department of Geology, University of California, Davis, California 95616-8605, U.S.A.

ABSTRACT—A new eosauropterygian genus and species is described from the middle Anisian (Middle Triassic) ofPanxian (Guizhou Province, southwestern China). The new taxon is characterized by an unique specialization of the jawsthat form an elongate pointed rostrum furnished with numerous small, monocuspid and vertically oriented teeth with abasally expanded crown and pointed tip, which is quite unlike any other sauropterygian known. Other diagnostic char-acters include: frontals paired; parietal unpaired; pineal foramen located centrally in broad parietal skull table; two carpalossification; ilium with distinct preacetabular process at the base of the dorsally extending iliac blade; pubis plate-like andof rounded contours; two tarsal ossifications. The curved and distally expanded humerus, the reversed topologicalrelationship of the clavicle and scapula, and the presence of three sacral ribs indicate sauropterygian affinities of the newtaxon, whereas the ‘butterfly-shaped’ or ‘cruciform’ facet for the neural arch on the dorsal centrum surface indicate itseosauropterygian status.

INTRODUCTION

The extensive Triassic outcrops of Guizhou Province, south-western China, have yielded a diverse fauna of marine reptilesthat includes ichthyosaurs (Li, 1999; Li and You, 2002; Yin et al.,2000; Nicholls et al., 2002; Chen and Cheng, 2003; Maisch et al.,2003; Jiang et al., 2003; Jiang, Hao, Maisch et al., 2005; Jiang,Schmitz, Hao et al., 2006; Jiang et al., 2007), thalattosaurs (Liu,1999, 2001; Yin et al., 2000; Liu and Rieppel, 2001, 2005; Luo andYu, 2002; Cheng, 2003; Jiang et al., 2004; Rieppel and Liu, 2006;Rieppel et al., 2000, 2006; Cheng et al., 2007), protorosaurs (Li,2003; Li et al., 2004), and sauropterygians. Among the sauro-pterygians recognized from the Middle and lower Upper Triassicof Guizhou Province are placodonts (Li, 2000; Li and Rieppel,2002; Yin et al., 2000), the pachypleurosaur genus Keichousaurus(Young, 1958; Lin and Rieppel, 1998; Cheng et al., 2004), theeusauropterygian nothosaur genera Nothosaurus and Lariosau-rus (Li et al., 2002; Li and Rieppel, 2004; Rieppel et al., 2003;Jiang, Maisch, Hao et al., 2005, 2006; Jiang, Maisch, Sun et al.,2006; Shang, 2006), and a pistosauroid (Cheng et al., 2006; thepossible pistosauroid Dingxiaosaurus luyinensis Liu et al., 2002,was declared a nomen dubium by Cheng et al., 2006; see also Li,2006). Here, we describe a new eosauropterygian taxon (sensuRieppel, 1994) from middle Anisian deposits of Panxian, south-western Guizhou Province, which is characterized by a uniquespecialization of its jaws, one that is quite unlike any other sau-ropterygian known to date (Rieppel, 2002). The premaxilla,maxilla and dentary are extended into an elongate pointed ros-trum, furnished with a large number of small, monocuspid, andvertically oriented teeth. The sauropterygian status of the taxonis indicated by the curved and distally expanded humerus(Storrs, 1991), the reversed topological relationship of the clavi-

cle and scapula (Carroll and Gaskill, 1985), and by the presenceof three sacral ribs, whereas the eosauropterygian affinities ofthe new taxon is indicated by the ‘butterfly-shaped’ or ‘cruci-form’ facet for the neural arch on the dorsal centrum surface(Rieppel, 1994).

Institutional Abbreviations—GMPKU, Geological Museumof Peking University, Beijing.

SYSTEMATIC PALAEONTOLOGY

Superorder SAUROPTERYGIA Owen, 1860Order EOSAUROPTERYGIA Rieppel, 1994

Family incertae sedisGenus WUMENGOSAURUS, gen. nov.

Type Species—Wumengosaurus delicatomandibularis, gen. etsp. nov.

Diagnosis—An eosauropterygian taxon of 95.5-130.5 cm totallength, with jaws forming an elongated and pointed rostrum fur-nished with a large number (in excess of 45-50) small teeth; teethwith basally expanded crown and pointed tip, positioned verti-cally; frontals paired; parietal unpaired; cheek partially coveredby broadened upper temporal arch; lower temporal arch absent;scapula with distinct posterodorsally extending blade, terminat-ing in a straight posterior margin; ilium with distinct preacetabu-lar process at base of distinct dorsally extending iliac blade; pubisplate-like, of rounded contours; two carpal (intermedium andulare) and tarsal (astragalus and calcaneum) ossifications.

Distribution—Middle Triassic (Anisian), southwestern China.

WUMENGOSAURUS DELICATOMANDIBULARIS,gen. et sp. nov.

(Figs. 1–6)

Holotype—GMPKU-P-1210, a completely articulated skel-eton in left lateral view (Figs. 1, 3, 5).*Corresponding author.

Journal of Vertebrate Paleontology 28(4):1055–1062, December 2008© 2008 by the Society of Vertebrate Paleontology

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Referred Specimen—GMPKU-P-1209, an articulated skel-eton with an incomplete skull (Figs. 2, 4, 6).

Diagnosis—same as for genus, of which this is the only knownspecies.

Type Horizon—Upper Member, Guanling Formation; co-nodont biozone of Nicoraella kockeli Tatge, 1956; middle Pelso-nian, middle Anisian, Middle Trassic (Yang et al., 1999; Sun,2006).

Type Locality—Yangjuan Village, Xinmin District, PanxianCounty, Guizhou Province, P.R. China.

Etymology—The genus name is derived from “WumengMountain”, where the fossil site is located. The specific epithet isderived from the Latin, delicatus for “not robust,” “delicate,”and mandibula for “jaw,” “mandible.”

MORPHOLOGICAL DESCRIPTION

Both the holotype (GMPKU-P-1210, Fig. 1) and the referredspecimen (GMPKU-P-1209, Fig. 2) come from the same locality

and horizon. They are represented by nearly complete and ar-ticulated skeletons of approximately 95.5 cm (holotype) and130.5 cm (referred) total length respectively (with the tip of thetail incomplete in both specimens). Of the total length, the headand neck comprise about 20% (referred) to 21.5% (holotype),the trunk 31% (referred) to 33% (holotype), and the tail theremaining 49% (referred) to 45.5% (holotype). Both specimensare referred to the same taxon as they share diagnostic postcra-nial characteristics such as a robust clavicle articulating on theanteromedial aspect of the scapula, the scapula carrying a dis-tinct posterodorsally extending blade, a curved and distally ex-panded humerus with an entepicondylar foramen, an ilium witha distinct preacetabular process, and two carpal and tarsal ossi-fications respectively.

Skull

The skull of the holotype, on which the following descriptionis based, is complete but laterodorsally compressed, which re-

FIGURE 1. Skeleton of the holotype of Wumengosaurus delicatomandibularis, gen. et sp. nov. (GMPKU-P-1210) from the Upper Member ofGuanling Formation (Pelsonian, Anisian, Middle Triassic) of Yangjuan Village, Xinmin District, Panxian County, Guizhou Province, People’ sRepublic of China. Scale bar equals 10 cm.

FIGURE 2. Skeleton of the referred specimen of Wumengosaurus delicatomandibularis, gen. et sp. nov. (GMPKU-P-1209) from the Upper Memberof Guanling Formation (Pelsonian, Anisian, Middle Triassic) of Yangjuan Village, Xinmin District, Panxian County, Guizhou Province, People’ sRepublic of China. Scale bar equals 20 cm.

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sulted in extensive breakage; the skull of the referred specimenis incomplete. The new taxon (Fig. 3) is unique amongst sauro-pterygians in that the maxilla and premaxilla are extended intoan elongate, slender and anteriorly pointed rostrum. Unfortu-nately, preservation is such that no sutural details of the rela-tionship of the maxilla and premaxilla relative to the nasal, pre-frontal, and external naris can be ascertained. The external narisis retracted to a position behind the midpoint of the distancefrom the tip of the rostrum to the anterior margin of the orbit. Aspreserved, it appears as a slit-like opening, but due to distortionof the skull its natural contours are difficult to determine. Thedorsal margin of the external naris is formed by the narrow andelongate nasal, which receives the pointed tip of the premaxillaposterior (nasal) process in a facet on its anterior end, locateddorsal to the external naris. Posteriorly, the nasal overlaps theanterior end of the frontal at a level just anterior to the anteriormargin of the orbit. Both nasals and frontals are paired.

The prefrontal is a large element located at the anterodorsalmargin of the orbit. It has a strongly convex lateral surface, andit tapers to a pointed tip anteriorly that may have entered theposteroventral margin of the external naris. The presence orabsence of a lacrimal cannot be ascertained, nor is the contact ofthe maxilla with the jugal within the ventral margin of the orbitidentifiable. No scleral ossicles are preserved in the orbit. Theparietal forms a relatively broad (i.e., unconstricted) skull tablewith a posteriorly concave occipital margin. The pineal foramenoccupies a central location in the parietal skull table, at the levelof the midpoint of the longitudinal diameter of the upper tem-poral fenestra. The fronto-parietal suture remains indistinct, butsome indication of an interdigitating suture appears identifiableat the level of the posterior margin of the orbit. A shallow con-cavity on the right margin of the parietal delineates the medialmargin of the right upper temporal fenestra, which correspondsin length to the medial margin of the left upper temporal fenes-tra. The left upper temporal fenestra is completely enclosed bybone, but the bone surface along its lateral margin is damaged,such that its original width could have been somewhat narrower.Anatomical details of the configuration of the elements in thetemporal region of the skull are difficult, indeed largely impos-sible, to ascertain. The dorsal exposure of the postfrontal can be

identified on the both left and right side of the skull, at theposterolateral corner of the orbit. The postfrontal carries a slen-der and tapering anterior dorsal process that lines the pos-terodorsal margin of the orbit. The weakly concave lateral mar-gin of the frontal broadly enters the dorsal margin of the orbitbetween the prefrontal and the postfrontal. The posterior marginof the orbit is incomplete due to a disruption of the originalrelations of the postfrontal, postorbital, and jugal. Below themore posterior part of the upper temporal fenestra, there is anindication of a fairly extensive dermal covering of the cheekregion that must in large parts be composed by the squamosal.Sutural details cannot be identified, however; the relations of thesquamosal to the postorbital, jugal, and quadratojugal (if pres-ent) remain obscure. The weakly concave ventral margin of thedermal covering of the cheek region indicates a reduced, andventrally open lower temporal fenestra. The posterior margin ofthe dermal covering of the cheek indicates a concave posteriormargin of the quadrate. The posterior concavity of the quadrateis not as pronounced as in pachypleurosaurs, however, nor doesthe mandibular condyle of the quadrate extend into a postero-ventral projection, as it does in pachypleurosaurs, where such aposterior quadrate process provides ventral support for the tym-panic membrane (Rieppel, 1989).

No morphological details are available for the braincase andocciput. Part of the dermal palate is exposed in the left orbit (Fig.3). The midline suture on the dorsal surface of the palate, and thesuture between the pterygoid and the palatine can be discerned.

The left hemi-mandible of the holotype is exposed in lateralview. It shows a straight ventral margin as it tapers to a slenderand delicate anterior end at the symphysis. The dorsal margin ofthe mandible shows a slight but distinct coronoid elevation nearthe posteroventral corner of the orbit. No sutural details arevisible on the lateral surface of the mandible that would allowthe identification of separate elements. The retroarticular pro-cess is short yet robust. As the mandibular condyle of the quad-rate lacks a posteroventral projection, the retroarticular processalso lacks the fenestra in its dorsal surface that accommodatesthe posterior quadrate process in pachypleurosaurs.

Dentition

The dentition of Wumengosaurus delicatomandibularis isunique amongst sauropterygians. The lateral margins of the pre-maxilla, maxilla, and dentary are lined by a palisade of small,monocuspid, and vertically positioned teeth (Fig. 3). There are inexcess of 45 to 50 tooth positions in both the upper and lowerjaws. The individual teeth show a characteristic morphology, inthat the basally expanded tooth crown is distinctly set off from abasal pedicel. Apically, the crown terminates in a blunt tip. Atleast in the larger teeth located toward the posterior end of thetooth row, the enamel covering the tooth crown shows distinctstriations.

Vertebral Column

The cervical vertebral column is fully disarticulated in the re-ferred specimen, such that a reliable vertebral count cannot beestablished. In the holotype, the axis neural spine is a little bitwider anteroposteriorly than the neural spines of the succeedingvertebrae. Due to crushing and dislocation of the elements in theoccipital region, the detailed morphology of the atlas remainsobscure. The cervical vertebral column is preserved in the holo-type in articulation from the axis through the 15th cervical ver-tebra (Fig. 1). A gap separates the cervical vertebral columnfrom the element we identify as the first dorsal vertebra. Giventhe size of this gap in relation to the size of posterior cervicalvertebrae, a total count of 18 to 19 cervicals seems likely. All thecervical vertebrae are tall and robust, only slightly increasing in

FIGURE 3. Skull of the holotype of Wumengosaurus delicatomandibu-laris, gen. et sp. nov. (GMPKU-P-1210). Abbreviations: a, angular; d,dentary; f, frontal; j, jugal; m, maxilla; n, nasal; p, parietal; pal, palatine;pt, pterygoid; pm, premaxilla; po, postorbital; pof, postfrontal; prf, pre-frontal; q, quadrate; sa, surangular; sq, squamosal. Scale bars equal 2 cm.

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size from front to back. The pre- and postzygapophyses areprominent, and overlap in a horizontally oriented articular sur-face (as seen in lateral view). The neural spines are relativelywide, their antero-posterior width slightly increasing posteriorly.Their dorsal margin is weakly concave. As preserved, the lateralsurface of the cervical vertebrae below the zygapophyseal articu-lations offers little morphological detail. On the eighth and ninthcervical vertebrae there is some indication of the para- and di-apophyseal articulations that are separated by the closed but notfully fused neurocentral suture. The cervical ribs have been dis-placed ventrally relative to the ventral margins of the centra.Crushing renders the identification of their contours very diffi-cult. Small anterior cervical ribs are, however, well exposed atthe ventral margin of the third and fourth cervical. They show avery well developed free-ending anterior process. The anterior-most cervical rib that can be identified is located at the anteriorend of the ventral margin of the third cervical.

Again in the holotype, the count of dorsal vertebrae is 30 (31dorsals if 18 cervicals are counted). In the anterior dorsal regionthe vertebrae are exposed in dorsal view, exhibiting broadly ex-panding postzygapophyses that overlap the narrower prezyg-apophyses. Between the 16th and 18th dorsal element, the ver-tebral column is twisted, exposing the more posterior vertebraein lateral view. This correlates with an increased height of theneural spines, which are, however, mostly abraded in the ante-rior dorsal region. The neural spines of the posterior dorsal ver-tebrae are tall and antero-posteriorly expanded, leaving only avery narrow gap between the neural spines of succeeding verte-brae. As far as can be ascertained in lateral view, the prezyg-apophyses face upwards and inwards in the posterior caudal re-gion, the postzygapophyses face downward and outward. Thesynapophyses for the rib articulations are relatively short, anddisplay an oval articular surface that faces postero-latero-ventrally. The last dorsal vertebra is slightly disarticulated rela-tive to the first sacral vertebra, thus incompletely exposing theweakly amphicoelous posterior surface of the centrum. The dor-sal ribs are single-headed, strongly curved in their proximalshoulder region, but only very slightly curved distally. Especiallyin the referred specimen, the dorsal ribs show a mild degree ofpachyostosis in the proximal shoulder region.

The sacrum comprises three vertebrae. They differ from theposterior dorsal vertebrae mostly in their neural spines, whichare slightly taller yet less antero-posterioly expanded, and hencemore widely separated from one another. The neural arches ofthe sacral (and of the anteriormost caudal) vertebrae have sepa-rated from the centra (both in the holotype and in the referredspecimen), indicating lack of fusion of the neurocentral suture.The dorsal surface of the centrum of the sacral (and anteriormostcaudal) vertebrae expose the ‘butterfly-shaped’ or ‘cruciform’facet for the reception of the neural arch that is characteristic ofthe Eosauropterygia (Rieppel, 1994). The sacral ribs are free,i.e., not fused, to the sacral vertebrae. The medial element is themost robust of the three sacral ribs. In the holotype, the first twosacral ribs have a slightly convex anterior margin, and a moredistinctly concave posterior margin, whereas the third sacral ribhas slightly concave anterior and posterior margins. The first twosacral ribs are more distinctly expanded proximally than distally,while the third sacral rib is distally more distinctly expanded thanproximally.

The holotype as well as the referred specimen both lack the tipof the tail. Based on the holotype, however, the tail of Wumen-gosaurus delicatomandibularis must have comprised more than48 vertebrae. Within the tail region, the neural arches have againseparated from the centrum both in the holotype and in thereferred specimen. It is interesting to note that in the cervicalregion of the holotype, as well as within the dorsal region of bothspecimens, the neural arches remain in articulation with the ver-tebral centra. This indicates an antero-posterior gradient in the

fusion of the neurocentral suture. Within the caudal region, theneural spines become progressively lower, antero-posteriorlynarrower, and increasingly posteriorly inclined. The last neuralspine is preserved on the 26th caudal vertebra. The followingthree caudals seem to lack a neural spine as a consequence ofincomplete preservation, but neural spines continue to be absenton the 30th and the succeeding caudal vertebrae. The referredspecimen shows various disarticulated caudal vertebral centra indifferent orientations, thus revealing concave lateral and ventralmargins of the central body as well as deeply amphicoelous in-tervertebral articulations. The caudal ribs are free, i.e., not fusedto the caudal vertebrae. Only two or three caudal ribs are pre-served in the holotype, but the referred specimen shows that atleast five anterior caudal vertebrae carried ribs. The caudal ribsare pachyostotic; they curve postero-laterally and decrease inlength from front to back. The first preserved chevron articulateson the posterior ventral surface of the centrum of the fourthcaudal vertebra in the holotype. The absence of more anteriorchevrons may be due to incomplete preservation, but the re-ferred specimen again shows no (disarticulated) chevrons in themost proximal tail region. The chevrons in general articulate atthe posterior end of the respective centra, although many haveshifted during preservation, and they decrease in size from frontto back. Again in the holotype, the last preserved chevron ar-ticulates on the 26th caudal vertebra. As is the case for the neuralarches, their absence on the following three vertebrae may bedue to incomplete preservation, but chevrons appear to be genu-inely absent on the 30th and the succeeding caudal vertebrae.

Gastral Rib

Gastral ribs are prominent in Wumengosaurus delicatoman-dibularis, each one comprising five elements: an angled midven-tral one, and two spindle-shaped collateral elements on eitherside. Although certainly not in perfect alignment, the anteriorgastral ribs are fairly regularly distributed in the holotype, sug-gesting the presence of two gastral ribs per body segment.

Pectoral Girdle and Forelimb

The pectoral girdle and forelimb are better preserved andmore completely exposed in the referred specimen (Fig. 4), onwhich the following description is mostly based. Being preservedin dorsal view, the vertebral column obscures the medioventralcontact of the clavicles (if present), as well as the interclavicle.But the lateral wings of both clavicles are exposed in dorsal view,and the left one in particular displays its expansive, pachyostoticstructure. The clavicle forms a weakly pronounced anterolateralcorner, from which originates a posteromedially extending hori-zontal flange. The posterodorsal process of the clavicle termi-nates in a blunt tip.

Both scapulae are well preserved and exposed in medial view.The scapula has an extended ventral (glenoid) portion, delimitedby a ventrally concave margin that participates in the formationof the dorsal part of the glenoid fossa. The ventral (glenoid)portion of the scapula is set off from the dorsal scapular blade bya distinct constriction. In contrast to other eosauropterygians,the dorsal scapular blade is expansive in Wumengosaurus deli-catomandibularis, slightly expanding posterodorsally and termi-nating in a straight posterior margin. On the anteromedial sur-face of its anteroventral extension the left scapula shows a dis-tinct facet (also present but less well preserved on the rightscapula) for the reception of the posterodorsal process of theclavicle. This indicates the presence of the reversed relation ofthe scapula and clavicle in Wumengosaurus delicatomandibu-laris, a synapomorphy this species shares with other sauropter-ygians (Carroll and Gaskill, 1985).

Only the anterolateral (glenoid) margin of the left coracoid is

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exposed in the referred specimen. The left coracoid is more com-pletely exposed in the holotype, but it is only poorly preserved,thus offering no relevant morphological detail.

The humerus is well exposed in both specimens (Figs. 1, 2, 4),the best preserved one being the left humerus of the referredspecimen (Fig. 4). The remarkable size difference of the humerus(Table) between the somewhat smaller holotype and the re-ferred specimen indicates its positive allometric growth. Thebone has the curved appearance that is characteristic of sauro-pterygians (Sander, 1989; Storrs, 1991). The humerus is distallymore distinctly expanded than proximally. Its anterior (preaxial)margin is convex, its posterior (postaxial) margin is more dis-tinctly concave. The deltopectoral crest is weakly developed. Theectepicondylar groove is distinct, which results in a shallow ect-epicondylar notch at the distal end of the humerus near its pre-axial margin. An entepicondylar foramen is present.

The best preserved zeugopodium and carpus are those of theright forelimb of the referred specimen, although the positions ofthe elements have been reversed during fossilization. Theslightly expanded proximal end of the radius is somewhat bentbackwards, which results in a characteristic angulation of its pre-

axial margin. The distal end of the radius is not expanded, itsanterior and posterior margins are straight and parallel relativeto each other. The ulna is more massively built and somewhatshorter than the radius. It is a straight element that is moreexpanded proximally than distally. The concavity of the preaxialmargin is more distinctly expressed than that of the postaxialmargin, which, together with the angulation of the proximal headof the radius, contributes to the formation of a spatium interos-seum between radius and ulna.

Two carpal ossifications are present in both hands of bothspecimens, which in their morphology show a striking similarityto the pachypleurosaur Neusticosaurus (e.g., Neusticosaurus ed-wardsii: Carroll and Gaskill, 1985, fig. 17). The ulnare hasrounded contours and lies distal to the ulna. The intermedium isa slender, elongate, indeed rectangular ossification. On the basisof the right manus of the referred specimen, the intermediummay be inferred to have been located distal to the ulna, interca-lated between the ulnare and the distal end of the radius (Fig. 4).

Of the five metacarpals, the first is the shortest, the third thelongest. The metacarpals in general are straight elements withconcave anterior and posterior margins and correspondingly ex-panded proximal and distal ends. As preserved, there is no evi-dence for a proximal overlap of the metacarpals. The phalangealcount remains unknown for Wumengosaurus delicatomandibu-laris.

Pelvic Girdle and Hind Limb

The ilium is highly characteristic for Wumengosaurus delica-tomandibularis, and quite unlike that of other sauropterygians.Well preserved on the left side of the holotype (Fig. 5), the iliumshows a ventrally expanded acetabular portion, delimited by aventrally convex margin that participates in the formation of theacetabulum. The ventral acetabular portion is set off from thedorsal iliac blade by a constricted neck region. The iliac blade isa dorsally ascending, slightly recurved, blade-like structure witha convex anterior, and a concave posterior margin. At mid-height of the dorsal iliac blade, a very prominent, anteriorlydirected pre-acetabular process projects from its anterior margin.

In the majority of Triassic eosauropterygians the pubis has adistinctly concave anterior and posterior margin, whereas itsventral (medial, symphyseal) margin is convex (Rieppel, 2000).This contrasts with the pubis in Wumengosaurus delicatoman-dibularis (Fig. 5), which is more of a plate-like structure ofrounded contours, thus reducing the size of the thyroid fenestra.The dorsal (lateral, acetabular), anterior, and ventral (medial,symphyseal) margins of the pubis are strongly convex, its poste-rior margin is very weakly concave. An obturator foramen can-not be identified, but it might be obscured by the overlappingacetabular portion of the ilium.

The ischium is again more of a plate-like structure than isotherwise characteristic of Triassic eosauropterygians. Its dorsal(lateral, acetabular) is somewhat narrower than its ventral (me-dial, symphyseal) part. Its posterior margin is irregularly convex,whereas its anterior margin is distinctly concave. The weaklyconcave posterior margin of the pubis together with the moredistinctly concave anterior margin of the ischium thus enclose areduced thyroid fenestra.

The femur of Wumengosaurus delicatomandibularis is straightwith proximally and distally expanded ends (Fig. 6). It is some-what longer than the humerus. Since the femur is preserved indorsal view in both specimens, the degree of differentiation ofthe internal trochanter cannot be ascertained. The articulationsfor tibia and fibula at its distal end are confluent.

The zeugopodium and autopodium of the hind limb show amorphology that is again very similar to the one observed inpachypleurosaurs. Best preserved is the left hind limb of thereferred specimen. The slightly curved fibula is a little longer

FIGURE 4. The pectoral girdle and forelimb of the referred specimenof Wumengosaurus delicatomandibularis, gen. et sp. nov. (GMPKU-P-1209). Abbreviations: cl, clavicle; co, coracoid; h, humerus; i, interme-dium; r, radius; sc, scapula; u, ulna; ul, ulnare. Scale bar equals 5 cm.

TABLE. Measurements (in mm) of Wumengosaurus delicatomandibu-laris, gen. et sp. nov.

MeasurementGMPKU-P-1210

(holotype)GMPKU-P-1209

(referred)

Length of mandible 82.5 —Length of left humerus 44 66.5Proximal width of left humerus 12.2 16.5Distal width of left humerus 14.8 24.5Length of radius 28.5 (left) 38 (right)Length of ulna 24 (left) 35.5 (right)Length of metacarpal 3 13 (left) 16.5 (right)Length of left femur 51 64.8Proximal width of left femur 12.3 13.5Distal width of left femur 12.8 14Length of left tibia 25.5 32.5Length of left fibula 27.5 35Length of metatarsal 3 15.5 (right) 19.5 (left)

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than the more robustly built tibia. The tibia is an essentiallystraight element, with its proximal end more distinctly expandedthan its distal end. The curved appearance of the fibula resultsfrom the fact that its preaxial margin is concave, its postaxialmargin convex. The concave preaxial margin of the fibula con-tributes to the formation of a spatium interosseum between itselfand the tibia.

Two tarsal ossifications are present in Wumengosaurus delica-tomandibularis, both of rounded contours (Fig. 6). The astraga-lus is located in an intermedium position. Its proximal marginshows a very slight concavity that marks the passage of the per-forating artery. The calcaneum is slightly smaller than the as-tragalus, and located distal to the fibula.

Of the five metatarsals, the third is again the longest, the firstthe shortest. The metatarsals are straight elements with concaveanterior and posterior margins and expanded proximal and distalends. The first metatarsal differs from the others in that its proxi-mal head is distinctly more expanded than its distal end. It is alsolarger relative to the fifth metatarsal, as compared to the firstmetacarpal which is much smaller compared to the fifth meta-carpal. As preserved, there is no proximal overlap of the meta-tarsals. None of the feet in either specimen preserves a completecomplement of phalanges. The phalangeal formula for the pestherefore remains unknown, too.

DISCUSSION

Wumengosaurus delicatomandibularis gen. et sp. nov. is a newsauropterygian from the middle Anisian of southwestern

Guizhou Province. The curved shape of the humerus, the re-versed relation between clavicle and scapula, the presence ofthree sacral ribs, and the ‘butterfly-shaped’ sutural facet on thecentrum for the reception of the neural arch pedicels indicateeosauropterygian affinities. The relatively short postorbital re-gion of the skull, the broad parietal skull table with a centrallylocated pineal foramen, and the relatively extensive dermal cov-ering of the cheek region exclude the taxon from the Eusauro-pterygia (sensu Tschanz, 1989). Instead, the new taxon sharessome interesting morphological similarities with pachypleuro-saurs.

Wumengosaurus delicatomandibularis is larger than mostpachypleurosaurs, but it approaches the size of the largest knownpachypleurosaur, viz. Neusticosaurus edwardsii, which can reacha total length of 120 cm (Carroll and Gaskill, 1985). The promi-nent development of the prefrontal, as well as the broad parietalskull table with a centrally located pineal foramen, are pachy-pleurosaur characters within the Eosauropterygia shared by Wu-mengosaurus delicatomandibularis. Fusion of frontals and/or pa-rietals is variable amongst pachypleurosaurs. In Keichousaurus,both frontals and parietals are fused; in others, such as Neusti-cosaurus edwardsii, the frontal is fused whereas the parietalsremain separate, in contrast to Wumengosaurus delicatoman-dibularis, where the reverse situation obtains. The upper tempo-ral fenestra is relatively large in Wumengosaurus delicatoman-dibularis, even accounting for some incompleteness of its lateralmargin, but the upper temporal fenestra is also relatively large inbasal pachypleurosaurs such as Keichousaurus, Anarosaurus,and Dactylosaurus (Rieppel and Lin, 1995; Rieppel, 2000). Inpachypleurosaurs, the degree of dermal covering of the cheekregion is correlated with the relative size of the upper temporalfenestra. Basal taxa with a relatively large upper temporal fenes-tra, such as those mentioned above, retain a relatively narrowupper temporal arch, which results in an open cheek region.Taxa with a much reduced size of the upper temporal fenestra,such as the species in the genus Neusticosaurus (Caroll and Gas-kill, 1985; Sander, 1989), show an expanded upper temporal arch,

FIGURE 5. The pelvic girdle of the holotype of Wumengosaurus deli-catomandibularis, gen. et sp. nov. (GMPKU-P-1210). Abbreviations: fe,femur; il, ilium; is, ischium; pu, pubis; sr, sacral rib. Scale bar equals 2 cm.

FIGURE 6. The hindlimb of the referred specimen of Wumengosaurusdelicatomandibularis, gen. et sp. nov. (GMPKU-P-1209). Abbreviations:as, astragalus; ca, calcaneus; fe, femur; fi, fibula; il, ilium; sr, sacral rib; ti,tibia. Scale bar equals 5 cm.

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which contributes to the dermal covering of the dorsal cheekregion. In that respect, Wumengosaurus delicatomandibularis isunique in that it combines a relatively large upper temporal fe-nestra with a broad upper temporal arch providing a dermalcovering of at least the posterior cheek region.

The number of cervical vertebrae in Wumengosaurus delica-tomandibularis corresponds well with that in pachypleurosaurs.In contrast, with 30 (31) dorsal vertebrae Wumengosaurus deli-catomandibularis exceeds the number of trunk vertebrae inpachypleurosaurs; the highest dorsal count amongst the latter is25 or 26 vertebrae in Anarosaurus. Wumengosaurus delicato-mandibularis also has a somewhat elevated number of caudalvertebrae by comparison to pachypleurosaurs.

The pectoral girdle and forelimb of Wumengosaurus delicato-mandibularis correspond well to the pachypleurosaur morphol-ogy, except for the broad and elongated dorsal scapular blade. Aparticularly striking similarity concerns the elongate and rectan-gular intermedium, which must have been located distal to theulna, intercalated between the distal end of the radius and theulnare. The pelvic girdle of Wumengosaurus delicatomandibu-laris is of a and the reduction of the thyroid fenestra, regardingits rounded plate-like pubis and ischium.

In order to more firmly establish the phylogenetic relation-ships of Wumengosaurus delicatomandibularis, we conducted aphylogenetic analysis based on the data matrix in Rieppel (1998).The analysis was rooted on an all-0-ancestor that served as theoutgroup. The in-group taxa included: Captorhinidae, Testu-dines, Araeoscelidia, Younginiformes, Kuehneosauridae, Rhyn-chocephalia, Prolacertiformes, Trilophosaurus, Choristodera,Archisauriformes, Claudiosaurus, Dactylosaurus, Sperpianosau-rus-Neusticosaurus, Simosaurus, Nothosaurus, Lariosaurus,Corosaurus, Cymatosaurus, Germanosaurus, Pistosaurus, Placo-dus, and Wumengosaurus. The coding of the 119 characters forWumengosaurus was as follows (in groups of five): 10000 000?00130? ?2001 11??? ?2??? ??0?? ?11?? ????? ??10? ??000 10?10????? 0?00? 11100 1???1 1??1? 10??? 011?1 00100 ?1?1? ?111100112 00??. We analyzed the matrix using PAUP* version 4.0b10for Macintosh, implementing a heuristic parsimony search thatyielded three equally parsimonious trees with a tree-lengthTL � 309 steps, a consistency index CI � 0.479, and a retentionindex RI � 0.7135. Lack of resolution was restricted to the basalarchosauromorph clades. Sauroptyerygian interrelationshipswere fully resolved, with Wumengosaurs coming out as sister-taxon to the ((Dactylosaurus) (Serpianosaurus-Neusticosaurus))clade. The generic affinity of Wumengosaurus with pachypleu-rosaurs within eosauropterygians is thus confirmed.

In summary, Wumengosaurus delicatomandibularis gen. et sp.nov. approaches pachypleurosaurs most closely amongst eosau-ropterygians in its morphology and phylogenetic relationships,but we hesitate to include the taxon in the family Pachypleuro-sauridae not only because of the morphological differences out-lined in the discussion above, but also because of its feedingspecialization. Pachypleurosaurs are characterized by a relativelyshort and broad snout, which is indicative of some form of suc-tion feeding (Rieppel, 2002). This stands in stark contrast toWumengosaurus delicatomandibularis, where the preorbital re-gion of the skull is much longer than the postorbital region, dueto the development of a slender and pointed rostrum. Wumen-gosaurus delicatomandibularis is thus characterized by the pos-session of highly differentiated ‘pincers jaws’ (sensu Taylor,1987), which in marine vertebrates are typically used to secureprey with a laterally directed snapping bite. Other sauropteryg-ians seem to have adopted a similar feeding strategy, such asnothosaurs and pistosaurs (Rieppel, 2002), but none has evolveda jaw morphology that would come close to the rostrum of Wu-mengosaurus delicatomandibularis. The latter is characterized byits slenderness, its pointed tip, and its homodont dentition. Theonly other Triassic marine reptile that shows a rostrum morphol-

ogy similar to that observed in Wumengosaurus delicatoman-dibularis is the thalattosaur Endennasaurus acutirostris from theNorian (Late Triassic) of Lombardy, Northern Italy (Renesto,1991). However, the rostrum of Endennasaurus is edentulate,and is referred to thalattosaurs in virtue of morphological char-acters that are absent in Wumengosaurus delicatomandibularisgen. et sp. nov. (Müller, Renesto and Evans, 2005).

ACKNOWLEDGMENTS

Miss Tian-fen Hu partially prepared the specimen. Project40672002 and 40302009 were supported by National Natural Sci-ence Foundation of China. DYJ was supported by the Programfor New Century Excellent Talents in University (NCET-07-0015). Grant 7886-05 was authorized from the Committee forResearch and Exploration of the National Geographic Society.Associate editor Robin O’Keefe, Constanze Bickelmann, andone anonymous reviewer offered welcome advice and com-ments.

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Submitted October 31, 2007; accepted April 26, 2008.

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