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cluding Xinpusaurus, which indicated that the genus was the sister group of the Upper Triassic (Carnian) thalattosaur Nec- tosaurus described by Merriam (1905 ...
Journal of Vertebrate Paleontology 24(1):80–88, March 2004 q 2004 by the Society of Vertebrate Paleontology

A NEW SPECIES OF XINPUSAURUS (THALATTOSAURIA) FROM THE UPPER TRIASSIC OF CHINA DA-YONG JIANG1, MICHAEL W. MAISCH2, YUAN-LIN SUN1, ANDREAS T. MATZKE2, and WEI-CHENG HAO1 1Geological Museum and Department of Geology, Peking University, Beijing 100871, People’s Republic of China, [email protected]; 2 Institut und Museum fu¨r Geologie und Pala¨ontologie der Universita¨t Tu¨bingen, Sigwartstr. 10, D-72076, Tu¨bingen, Germany, [email protected]

ABSTRACT—A new species of Xinpusaurus Yin in Yin et al., 2000 (Thalattosauria, Thalattosauridae), is described from the Wayao Member of the Falang Formation (Tuvalian, Carnian, Upper Triassic) of Guanling County in Guizhou, southwestern China. It is the third thalattosaur species known from the Guanling faunal assemblage of marine reptiles. The type and only specimen consists of an entire skeleton, including a complete skull. It differs from the type species, X. suni, by its smaller adult size, the larger nasal, the more slender angular and low retroarticular process, the shape of the cervical neural spines, the number of presacral vertebrae, the large size of the scapula, the shape of the radius, the presence of a well ossified carpus, the more slender femur, the smaller hindfin, the presence of a complete row of distal tarsal ossifications, and the proportions of the metatarsals. It is consequently referred to a new species, Xinpusaurus kohi. A new analysis of thalattosaur interrelationships based on 30 cranial and postcranial characters corroborates a sister-group relationship between Xinpusaurus and Nectosaurus from the Carnian of California.

of features, particularly in the postcranial skeleton, allowing it to be recognized as a new species. The purpose of this study is to provide a description of this new thalattosaur and to assess the phylogenetic position of the genus Xinpusaurus within the Thalattosauria. Institutional abbreviations GMPKU, Geological Museum of Peking University, Beijing; GMR, GGSR, collections at the Geological Survey of Guizhou, Guiyang; IVPP, Institute for Vertebrate Paleontology and Paleoanthropology, Academia Sinica, Beijing; UCMP, University of California Museum of Paleontology, Berkeley.

INTRODUCTION Recently, two new genera and species of Upper Triassic thalattosaurs were described from the Carnian (Tuvalian) Wayao Member of the Falang Formation of Guizhou Province in southwestern China. One of them, Anshunsaurus huangguoshouensis Liu, 1999 was first incorrectly described as a pistosaurid sauropterygian (Liu, 1999), before Rieppel et al. (2000) clarified its status as a thalattosaur and suggested a close relationship to the Middle Triassic basal thalattosaur Askeptosaurus italicus. A second genus and species of thalattosaur was shortly described by Yin (in Yin et al., 2000) as Xinpusaurus suni on the basis of four articulated skeletons. It was incorrectly attributed to the ichthyosaur family Cymbospondylidae (see Maisch and Matzke, 2000, for the most recent diagnosis and definition of this ichthyosaur family, with which Xinpusaurus shares no derived features). Liu and Rieppel (2001) described an isolated thalattosaur skull from the Falang Formation, which they attributed, in our opinion correctly, to Xinpusaurus cf. X. suni. They provided a phylogenetic analysis of thalattosaur relationships, including Xinpusaurus, which indicated that the genus was the sister group of the Upper Triassic (Carnian) thalattosaur Nectosaurus described by Merriam (1905, 1908) and Nicholls (1999). An incomplete skull and postcranium was referred to the same taxon by Liu (2001). Most recently, Luo and Yu (2002) redescribed the skull of the holotype of X. suni (GMR 010) and a new very well-preserved three-dimensional skull (GGSR 001) of Xinpusaurus suni. Their description deviates from that of Liu and Rieppel (2001), but personal observation of both the specimen examined by Liu and Rieppel (IVPP V 11860) and those described by Luo and Yu, as well as our study of additional specimens at the collections of the Geological Survey of Guizhou and Peking University indicates that Luo and Yu’s (2002) description is essentially correct, and also applies to the other known specimens of X. suni. It is therefore taken as a basis for comparison, as far as the skull of this taxon is considered. Here, we report a third thalattosaur species from the Falang Formation; it can be referred to the genus Xinpusaurus but is distinguished from the type species by a considerable number

SYSTEMATIC PALEONTOLOGY Order THALATTOSAURIA Merriam, 1905 Family THALATTOSAURIDAE Merriam, 1905 Genus XINPUSAURUS Yin in Yin et al., 2000 Type-species Xinpusaurus suni Yin, 2000 (see Yin et al., 2000, pls. VII–VIII for figures of the type material). Emended Generic Diagnosis Large thalattosaur with moderately long, straight or slightly dorsally bent pointed rostrum (about 50–60% of skull length); anterior end of maxilla curved dorsally, carrying enlarged procumbent teeth; anterior teeth (on premaxilla, anterior part of maxilla and dentary) conical and pointed, more posterior teeth blunt; small diastema between premaxillary and maxillary teeth; nasal forming entire dorsal margin of external naris, maxilla forming ventral narial margin, premaxilla excluded from naris; premaxilla sending wide, long process posteriorly below external naris; posterolateral frontal process slender, extending posterior to anterior margin of lower temporal fenestra, meeting supratemporal; vomer and pterygoid dentigerous; strong overbite between upper and lower jaw; slender mandible with dentary symphyseal region tapering to narrow tip; surangular about 2/3 length of mandible, dentary very short; about 35–40 presacral vertebrae; neural spines of presacral vertebrae rectangular and wide; neural spines of sacral vertebrae narrow and straight; neural spines of anterior caudal vertebrae very slender and narrow; all caudal neural spines inclined posteriorly; about 94 tail vertebrae; haemapophyses of

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JIANG ET AL.—NEW THALATTOSAUR FROM CHINA similar length to neural spines, not markedly elongated; scapula slender; radius and fibula strongly widened. XINPUSAURUS KOHI, sp. nov. (Figs. 1–3) Holotype GMPKU 2000/005, complete articulated skeleton (Figs. 1–3). Type Locality Xinpu village, Guanling County, Guizhou Province, People’s Republic of China. Type Horizon Wayao Member of the Falang Formation, Tuvalian, Carnian, Upper Triassic. Derivatio Nominis After Ting-pong Koh, one of the pioneers in the study of fossil reptiles from China. Diagnosis Distinguished from Xinpusaurus suni by the following features: adult size less than 150 cm; nasal more extensive posteriorly; angular very low and narrow; processus retroarticularis of mandible low; neural spines of cervical vertebrae wider and more closely spaced; only 35 presacral vertebrae at maximum; scapula much larger than humerus; radius with distinct anteroproximal notch; carpus well ossified; femur with narrow proximal end; fibula slightly wider than long; tarsus completely ossified with two proximal and at least four distal tarsals; metatarsals two to five of similar length; stylo- and zeugopodial portion of hindlimb only about 10% larger than forefin. DESCRIPTION The skeleton is almost completely preserved in left lateral view (Fig. 1). The left fore- and hindlimbs are slightly disarticulated but almost complete (Fig. 3B, C). Of the shoulder girdle, only the left scapula and both clavicles can be identified. The vertebral column is complete and, except for anteriormost neck vertebrae, retains its natural articulation (Fig. 1). The skull shows both its left lateral side and the dorsal surface of the skull roof (Figs. 2, 3A). It is complete and well articulated. The most striking feature of the skull is the moderately elongate but narrow rostrum. The entire skull length is 19.6 cm; the snout length (measured from the anterior tip of the rostrum to the anterior orbital margin) is 11.6 cm, so that the snout amounts to more than 50% of the entire skull length. It is slightly longer than in the type of Xinpusaurus suni (Yin et al., 2000; Luo and Yu, 2002; pers. obs.), but as there is apparently some variation in that species, which is known from numerous complete skulls and skeletons (Yin et al., 2000; Liu, 2001; Liu and Rieppel, 2001; Luo and Yu, 2002) this is not considered to be taxonomically relevant. The anteriormost part of the premaxillary rostrum, which is slightly displaced with respect to the rest of the skull, is very pointed and edentulous. The first clear tooth remains are found 48 mm from the tip of the snout. This is a similarity to the holotype and other referred specimens (Yin et al., 2000; Luo and Yu, 2002; pers. obs.) of X. suni. As in X. suni there is no indication of a ventral deflection of the rostrum (Luo and Yu, 2002; pers. obs. contra Liu and Rieppel, 2001), instead it is completely straight. In the holotype and other referred specimens of X. suni (Yin et al., 2000; Luo and You, 2002; pers. obs.) the anterior tip of the rostrum is even deflected somewhat dorsally, as best seen in GGSR001 (pers. obs.). Only five premaxillary teeth can be clearly identified, but they are too damaged to be certain about their morphology, except that they are of a conical shape. → FIGURE 1. Holotype skeleton of Xinpusaurus kohi, sp. nov. (GMPKU 2000/005) from the Wayao member of the Falang Formation (Carnian, Tuvalian) of Xinpu, Guanling County, Guizhou Province, People’s Republic of China. Scale bar equals 50 mm.

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FIGURE 2.

Skull of the holotype of Xinpusaurus kohi, sp. nov. (GMPKU 2000/005). Scale bar equals 20 mm.

There is only a slight step formed between the alveolar margins of the premaxilla and maxilla. The alveolar margin of the maxilla protrudes further ventrally than that of the premaxilla, the same is true for X. suni (Luo and You, 2002; pers. obs. contra Liu and Rieppel, 2001). The premaxilla sends a wide, posterior process posteriorly below the external naris which extends almost to the posterior narial margin. This is also the case in X. suni, where this feature is particularly well preserved in the holotype (Luo and Yu, 2002; pers. obs.). The maxilla sends a very narrow process anteriorly, dorsal to the posterior premaxillary process, which meets the anteriormost extension of the nasal and thus excluded the premaxilla from the external naris. The alveolar margin of the maxilla is more or less straight. Only one anterior maxillary tooth can be identified. It is clearly procumbent, as in other Xinpusaurus specimens (Liu and Rieppel, 2001). Posterior to the naris the maxilla sends a short, triangular postnarial process posterodorsally, which meets the prefrontal and frontal and separates them from the nasal and external naris. The nasal is an unusually extensive element which, as in X. suni (Luo and Yu, 2002; pers. obs. contra Liu and Rieppel, 2001) forms the entire dorsal margin of the external naris. It is in contact with the premaxilla anterolaterally and medially, the maxilla laterally, and the frontal posteromedially. It remains separated from the prefrontal by a clear maxilla-frontal contact. The prefrontal is large and develops a strong, anterolateral shield-like projection, which covers the anterodorsal corner of the orbit. It forms the anterior third of the dorsal orbital margin. The frontal is extensive. Its anteromedial processes are covered by the right nasal, so that the nasals appear to meet in the midline. This is, however, due to deformation. The anterolateral process is narrow and pinched in between the prefrontal and maxilla laterally and the nasal medially. It does not reach the posterior margin of the external naris. Posteriorly the frontal forms most of the skull roof. The posterolateral process is, as in X. suni (Luo and Yu, 2002; pers. obs. contra Liu and Rieppel, 2001) very extensive and ends posteriorly in a pointed tip, about half way along the length of the lower temporal fenestra. It establishes at least a point-contact with the supratemporal. An extensive contact between supratemporal and frontal is also present in the specimen of X. cf. X. suni described by Liu and Rieppel (2001), and it is also seen in the material described by Luo and Yu (2002) in contrast to their description and figures (pers. obs.). The postorbital and postfrontal are fused. The postorbitofrontal sends a narrow process anteriorly, which extends along

the posterior third of the dorsal orbital margin but fails to reach the prefrontal. The frontal thus clearly contributes to the dorsal margin of the orbit. The postorbital process of the postorbitofrontal is straight and very narrow. The jugal is ill-preserved. It is a slender, triradiate element. The posterior part of the skull table is not well preserved and shows few details. The skull table shows a deep rectangular sagittal indentation, which contrasts with the more rounded sagittal concavity reconstructed by Liu and Rieppel for X. suni (2001). As demonstrated by specimen GMPKU 2000/002 of X. suni, as well as GGSR001 described by Luo and Yu (2002), which both show the dorsal view very well, the concavity is in fact also of more rectangular shape in that species. The parietal foramen is small and situated only 5 mm from the posterior margin of the skull table. This contrasts with the situation described by Liu and Rieppel in X. suni (2001), which assumes an anteriorly displaced parietal foramen, situated close to the fronto-parietal suture, in Xinpusaurus. As specimens GMPKU 2000/002 and GGSR001 (Luo and Yu, 2002) also clearly show a posteriorly displaced parietal foramen it appears possible that either this feature is variable in Xinpusaurus, or that Liu and Rieppel (2001) are mistaken on this point. As the parietal foramen is not very clear in their specimen (Liu and Rieppel, 2001:81; pers. obs.) the latter alternative appears to be likely. The massive quadrate is slightly dislocated and visible in posterolateral view. The posterior margin is deeply emarginated. The transversely expanded condyle is narrower than the dorsal extremity of the bone. The right quadrate and the lateral wall of the skull roof of the right side are also exposed in medial view. The medial surface of the quadrate is flat. The supratemporal can be seen to form the dorsomedial articulation for the quadrate. The basioccipital condyle, which is slightly expanded transversely and not markedly convex, is exposed posterior to the left quadrate. The left mandibular ramus is complete, except for the anteriormost tip of the dentary (Figs. 2, 3A). As shown by the holotype and other specimens (Yin et al., 2000; Luo and Yu, 2002; pers. obs.) Xinpusaurus suni has a clear overbite. In the holotype the premaxillary rostrum extends beyond the anterior end of the lower jaw for 30 mm. In the present specimen, the premaxillary rostrum extends about 60 mm anterior to the toothbearing portion of the dentary. If mandibular morphology and proportions are assumed to have been similar in both species in this respect, X. kohi probably also possessed a considerable overbite. The mandible is more slender than in the type species. The anterior end of the mandible is developed as an edentulous, pointed rostrum, the anteriormost tip of which is missing. The

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FIGURE 3. Details of the holotype of Xinpusaurus kohi, sp. nov. (GMPKU 2000/005). A, skull and mandible; B, forelimb and shoulder girdle; C, hindlimb. Abbreviations: a, angular; bo, basioccipital; c, clavicle; co, coronoid; d, dentary; f, frontal; fe, femur; fi, fibula; h, humerus; j, jugal; mx, maxilla; n, nasal; p, postorbitofrontal; pa, parietal; pmx, premaxilla; q, quadrate; r, radius; rib, cervical rib; sa, surangular; sc, scapula; st, supratemporal; u, ulna; v, cervical vertebral centrum. Scale bar equals 10 mm.

dentary, coronoid and surangular can be clearly identified. The surangular extends far anteriorly, beyond the level of the posterior end of the tooth row, and forms a triangular anterior suture with the dentary, as in the type species (Luo and Yu, 2002; pers. obs. contra Liu and Rieppel, 2001). The coronoid process is exclusively formed by the coronoid. It forms about one fourth the height of the entire lower jaw ramus. The retroarticular process is low and narrow. It is largely formed by the surangular. The angular is only a narrow strip of bone, which can be followed from the level of the orbit to the posterior end of the mandible. Fourteen teeth can be identified in the left dentary. This is probably close to the original number. All teeth are closely spaced. They are clearly arranged in two groups. The anterior

group consists of seven relatively large teeth (one could be a replacement tooth) so that the number of anterior dentary teeth is identical to the number given for X. suni by Liu and Rieppel (2001) with elongate and pointed crowns. The largest of these teeth, which occupies the fourth position, has a length of at least 8 mm. The posterior seven teeth are much smaller, being only about 3–4 mm in length. Their crowns have blunt tips. The ventral margin of the lower jaw is slightly concave ventral to the largest dentary teeth, whereas farther posteriorly it is convex. The step between the symphyseal region and the posterior portion of the lower jaw is slight. The entire jaw thus displays a sinusoidal curvature. The cervical vertebral column has become disarticulated anteriorly, but the neural spines from the axis backwards retain

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their natural articulation and therefore allow a reliable count of the presacral vertebrae to be made. The cervical centra have rounded articulatory surfaces, which are deeply concave as shown by probably the anteriormost two (atlas and axis), which lie dislocated posterior to the skull. A slender bone that covers part of the articular surface of one of the first cervical vertebrae represents a cervical rib (Fig. 3A). It is clearly double headed with a large tuberculum and small capitulum. Dicephalous cervical ribs were suggested by Liu (2001) for X. suni, although they could not be unequivocally demonstrated. The neck appears to have been short, as described by Liu (2001), consisting of only four or five cervical vertebrae. The neural spines of the presacral vertebrae are largely rather short and wide with a rectangular shape. There is only a narrow gap between the spines of adjacent vertebrae. This is in contrast to the type and referred specimens of X. suni (Yin et al., 2000; pers. obs.), as well as to the specimen described by Liu (2001) and the other specimens of Xinpusaurus in the GMPKU collection, which have considerably narrower and more widely spaced cervical and anterior thoracal neural spines. The neural spines are not closely sutured to the cervical centra, as the cervical and some of the anterior thoracal neural spines have become detached from their respective centra, although they retained their natural articulation from the second cervical onwards. There are only 33 vertebrae that can be clearly identified as presacrals. Even if one allows for two or three vertebrae to be missing from the slightly disarticulated cervical vertebral column (this appears unlikely considering the otherwise perfect state of articulation of the specimen), the number of presacrals is significantly lower than in X. suni which has at least 40 presacrals (Yin et al., 2000; pers. obs.). The trunk ribs are short, being about 85 mm in maximum length and only slightly curved. This yields a very slender body shape to the animal. There are two sacral vertebrae that are distinguished from the thoracals by their widened but short ribs. The neural spines of the sacrals are similar to those of the thoracals. The caudal vertebral column consists of 93 vertebrae. This seems to come close to the true number, as the holotype of X. suni (pers. obs.) shows 94 caudal vertebrae, as does specimen GMPKU 2000/ 001, both of which also preserve complete caudal vertebral columns. The caudal vertebrae are similar in shape to the thoracals, but the neural spines are deflected posteriorly and decrease markedly in size posteriorly. The well-developed haemapophyses are of similar length to the neural spines. Together with the slightly laterally compressed centra, the elongate neural spines and haemapophyses give the tail a laterally compressed appearance, as pointed out by Liu (2001). Of the shoulder girdle (Fig. 3B), both clavicles and the left scapula are identifiable, but are less well preserved than in the holotype of X. suni (Yin et al., 2000) and the specimen IVPP V 12673 described by Liu (2001). The scapula appears to have been slender, and the clavicle robust and curved for almost 908, as described by Liu (2001). The scapula agrees in shape with that of X. suni; it is, however, much larger. It is much longer than the humerus in GMPKU 2000/005 and identical in length to that of the type of X. suni, which is a much larger animal and in which the scapula is considerably smaller than the humerus (Yin et al., 2000; pers. obs.). The humerus is moderately elongate and stout. Both humeri are preserved, but the right one is covered by ribs and much deformed, whereas the left one is complete (Fig. 3B). Its proximal and distal ends are widened, the proximal end considerably more so than the distal end. The shaft is slightly constricted. Articular surfaces are not well defined either proximally or distally. The distal articulation surface is concave, as in the specimen of X. suni described by Liu (2001).

The zeugopodial elements are preserved in natural articulation (Fig. 3B) and corroborate the identifications of Liu (2001). The radius is much expanded. Its proximal end differs in shape from the specimen described by Liu (2001), as well as the holotype of X. suni and referred specimens of Yin et al. (2000), as it has a deep anteroproximal notch. The anterior margin of the radius is strongly convex, whereas the posterior margin is deeply concave. The radius therefore encloses a considerable spatium interosseum with the comparatively much more slender ulna, which is slightly expanded proximally and distally. There are two large and several small rounded carpal ossifications, which must belong to both forelimbs. The carpus is too disarticulated to be certain of its identification, but in the holotype and referred specimens of X. suni (Yin et al., 2000) there is no evidence of ossified carpals, even though the holotype is much larger. This is a very significant osteological difference. Much of the left autopodium is also preserved in good articulation (Fig. 3B). The left femur is complete (Fig. 3C). It differs considerably from that of X. suni by its very narrow proximal end, whereas the distal end is much expanded in both species. In X. kohi the distal end of the femur is more than twice as wide as the proximal end. In the type of X. suni (Yin et al., 2000; pers. obs.) the proximal end of the femur has two-thirds the width of the distal end. The same is the case in the specimen described by Liu (2001:fig. 1). The zeugopodial elements are moderately well preserved. The fibula is wide and short. It is slightly wider than long, being thus even shorter and wider than that of X. suni (Yin et al., 2000; Liu, 2001). The tibia retains an elongate, terrestrial shape. Its proximal end is considerably wider than the distal end. There appear to be two large and at least four small tarsal ossifications. This is in strong contrast to the much larger type specimen (total length 233 cm versus 135 cm for GMPKU 2000/ 005) of X. suni, where only two large proximal ossifications can be identified (Yin et al., 2000:pl. 8, fig. 4; pers. obs.), here tentatively identified as astragalus and calcaneum. Three large and at least 8 smaller ossifications are identifiable in GMPKU 2000/005 (Fig. 3C). Assuming that the tarsals of both hindfins have become mixed up in the specimen, this yields a minimal number of at least 6 ossified tarsal elements, two large proximal and four small distal tarsals, for the specimen. This is a fundamental osteological difference from the type of Xinpusaurus suni, as well as all other accessible specimens, which have hindlimbs reasonably well preserved but never show more than two tarsal ossifications. It is also a clear indication that GMPKU 2000/005 can be considered as an adult. The five left metatarsals are all preserved close to their natural position (Fig. 3C). The first metatarsal is shortest, the following four are all of similar lengths. This is distinctly different from the holotype of Xinpusaurus suni, in which the metatarsals increase continuously in length from the first to the fifth. Several long, slender, elongate phalanges are also present, but they are so dislocated that the phalangeal formula remains uncertain. DISCUSSION It is evident that the specimen described above represents a thalattosaur. The Thalattosauriformes, including Endennasaurus (Renesto, 1992), Askeptosaurus (Kuhn-Schnyder, 1952, 1971) and the Thalattosauria sensu Merriam (1905) were diagnosed by Nicholls (1999) on the basis of four unequivocal synapomorphies: the presence of an elongate premaxillary rostrum, the presence of an elongate processus retroarticularis of the mandible, distinctive caudal vertebrae with high, posteriorly inclined neural spines, and an ilium with a narrow, posteriorly angled iliac blade. All of these characters are found in X. suni

JIANG ET AL.—NEW THALATTOSAUR FROM CHINA (Yin et al., 2000; Luo and Yu, 2002; pers. obs.), and the first three are also present in GMPKU 2000/005. Additional characters, not recorded in Endennasaurus, are cited by Nicholls to support monophyly of this clade. They are: a small and narrow supratemporal fenestra, a supratemporal bone that lies deep, along the lateral surface of the parietal, and a skull that is posteriorly emarginated with the occiput situated anterior to the mandibular articulation. All of these features are shown by X. suni (Yin et al., 2000; Liu and Rieppel, 2001; Luo and Yu, 2002; pers. obs.) and by GMPKU 2000/005, so there can be no doubt that it is a thalattosaur. As the thalattosaurian status of Endennasaurus (Renesto, 1992) is slightly controversial, we have excluded this taxon from further comparison. Within the Thalattosauriformes (sensu Nicholls, 1999), GMPKU 2000/005 clearly belongs to the genus Xinpusaurus, as it shares numerous synapomorphies with X. suni, including the characteristic shape of the snout, with a long and pointed, straight, edentulous premaxillary rostrum, a premaxilla with an expanded posterior subnarial process, large nasals that form the dorsal margin of the external naris and exclude the premaxilla, a frontal with an elongated posterolateral process that extends beyond the anterior margin of the lower temporal fenestra and establishes a point-contact with the supratemporal, and a dentition with a combination of pointed anterior and blunt posterior teeth in the dentary, pointed teeth in the premaxilla, and procumbent, pointed anterior maxillary teeth. The only significant difference that is, at the present state of knowledge, apparent between the skulls of the two species, is the more slender lower jaw of X. kohi. This is due to the presence of only a narrow and short angular, which also yields a narrow, dorsoventrally compressed shape to the retroarticular process. The posterior extension of the nasal is also larger in X. kohi than it is in the type species of the genus. The postcranial skeleton of X. kohi is also similar to that of X. suni in the shape and proportions of the vertebral centra, the shape and proportions of the major fin elements, and many other features. However, there is also a number of considerable differences. Whereas in Xinpusaurus suni the neural spines of the cervical and anterior thoracal vertebrae are very elongate and narrow, with wide spaces left between the individual neural spines, they are shorter and closely spaced in X. kohi. The number of presacral vertebrae in X. suni is at least 40, whereas it is at maximum 35 in X. kohi. The scapula is much larger than in X. suni. The forelimb differs in the shape of the radius, which has a clearly defined anteroproximal notch. In contrast to that of X. suni, the carpus is well ossified. In the hindlimb, the tarsus is also completely ossified in X. kohi, although it is little more than half the size of the holotype of X. suni, which only has the astragalus and calcaneus ossified. The complete ossification of the carpus and tarsus also clearly indicates that GMPKU 2000/005 is an adult, and that X. kohi therefore was a clearly smaller species than X. suni, which probably did not exceed 150 cm in length. The femur differs considerably from that of X. suni, as it has a very narrow proximal end. The fibula is wider than long, whereas the opposite is true in X. suni. The hindlimb is, judging from the stylo- and zeugopodial elements, only about 10% larger than the forelimb, whereas it is considerably larger in X. suni. The proportions of the metatarsals are also quite different. They increase continuously in length from the first to the fifth in X. suni, whereas in X. kohi, the first is clearly the shortest, but metatarsals two to five are very similar in length. With respect to these differences in all major parts of the postcranial skeleton it is evident that GMPKU 2000/005 is not conspecific with the type of X. suni, and it is consequently made the holotype of a new species of Xinpusaurus. The question of the phylogenetic placement of Xinpusaurus has previously only been addressed by Liu and Rieppel (2001).

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They conducted an analysis of thalattosaur relationships, introducing Xinpusaurus in a data matrix published by Rieppel et al. (2000) that was extended by two additional characters. Their analysis yielded three most-parsimonious trees with a length of 30 steps, a consistency index of 0.733 and a retention index of 0.692. After deleting the very incompletely known genera Agkistrognathus and Paralonectes from the Middle Triassic of British Columbia (Nicholls and Brinkman, 1993) they also obtained three most-parsimonious trees with a consistency index of 0.759, a retention index of 0.696, and a length of 29 steps. In the strict consensus trees for both analyses, Xinpusaurus was found to occupy a sister-group position to Nectosaurus, and both genera formed the sister group to Clarazia, Hescheleria, and Thalattosaurus. Anshunsaurus and Askeptosaurus were the successive plesiomorphic sister groups of this assemblage, which Liu and Rieppel (2001) call the claraziids, extending the concepts of the Claraziidae envisaged by Peyer (1936a) and Rieppel (1987). The phylogenetic analysis of Liu and Rieppel (2001) suffers from two shortcomings. First, their account of the skull of Xinpusaurus, and therefore their character codings, are now known to be incorrect in a number of cases, as has been emphasized in the description of the skull of X. kohi given above, as well as by Luo and Yu (2002). Second, their analysis is based exclusively on 18 characters of the cranial skeleton and dentition, completely ignoring the wealth of data known on the postcranial skeleton of most thalattosaurs (Merriam, 1905; Peyer, 1936a, b; Kuhn Schnyder, 1952; Rieppel, 1987; Nicholls, 1999). We therefore decided to carry out a new analysis of thalattosaur relationships, including Xinpusaurus. It was conducted with the aid of the computer program PAUP* 4.0b10 for Windows. A heuristic search with all usual default settings in effect was carried out, and the tree was rooted on an all-zero ancestor. The core of the data matrix was taken from the papers of Rieppel et al. (2000) and Liu and Rieppel (2001), but we also took some characters from Nicholls (1999) to supplement the data set. Paralonectes and Agkistrognathus were excluded from the analysis, because of incomplete knowledge of their osteology, as suggested by Liu and Rieppel (2001). Character 4 of the original matrix of Liu and Rieppel (2001) therefore became an autapomorphy of Thalattosaurus and was excluded as uninformative from the data matrix. Twelve new characters of the cranial and postcranial skeleton were added to the original data matrix, and Xinpusaurus was recoded according to the new observations presented here. The coding for character 13 of Liu and Rieppel (2001) for Thalattosaurus was also changed from 1 to 2. Nicholls (1999) claims there is a slit-like supratemporal fenestra in Thalattosaurus. However, Merriam (1905) did not find any evidence for such an opening in that genus. Specimen UCMP 9084 of Thalattosaurus alexandrae, which preserves a well articulated temporal region, does not show any evidence for a temporal fenestra (see the illustrations in Nicholls, 1999, who claims that such a fenestra exists in the genus). That a slit between supratemporal and postorbitofrontal is present in specimen UCMP 10926 of the same species (Nicholls, 1999:fig. 2) could be a taphonomic artifact. The posterolateral skull roof elements of thalattosaurs are not well articulated. A similar ‘‘slit’’ can, as confirmed by pers. obs., be seen in specimen IVPP 12673 of Xinpusaurus suni described by Liu (2001), although none of the known specimens of Xinpusaurus otherwise shows indication of an upper temporal fenestra, not even small juveniles such as GMPKU 2000/002. There is thus no more evidence for the existence of a supratemporal fenestra in Thalattosaurus than there is in Nectosaurus or any other derived thalattosaur, but with specimen UCMP 9084 there is strong evidence to the contrary.

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Clarazia was recoded with a question mark for character six of the original matrix (character 5 in our data matrix) as the prefrontal-nasal region is not well preserved in the single known specimen, and Rieppel’s (1987) drawing of the original skull and his reconstruction are at variance. Thalattosaurus was coded for the plesiomorphic state (anteromedial processes of frontals shorter than anterolateral ones) for character 9, as suggested by Rieppel et al. (2000), whereas Liu and Rieppel (2001) coded it for the derived state, for which there is no evidence (probably a typographic error). Some character codings had to be changed for Xinpusaurus as compared to Liu and Rieppel’s (2001) interpretation. For their character 2—tip rostrum straight (0) or deflected ventrally to a variable degree (1)—Rieppel and Liu (2001) coded Xinpusaurus for the derived state. However, reinvestigation of their specimen (IVPP V11860) has shown that the apparent ventral deflection of the premaxillary rostrum, which is furthermore incompletely preserved in that specimen, is most likely the result of deformation. This is corroborated by the study of Luo and Yu (2002), by personal observation of additional specimens, including the holotype of X. suni, and also by the above description of X. kohi. In fact, the rostrum is either straight or even slightly deflected dorsally in Xinpusaurus, an unusual condition in thalattosaurs. Liu and Rieppel (2001) also claim that there is no diastema between the premaxillary and maxillary dentition of Xinpusaurus. In fact there is a small diastema in their specimen, as well as a larger one in the holotype of X. suni (pers. obs.; compare Luo and Yu, 2002, although their skull reconstruction is misleading on this point). Character 5 of Liu and Rieppel (2001, character 4 in our matrix due to the removal of the redundant original character 4), i.e., posterior dentary and maxillary teeth conical and pointed (0) or blunt (1), was originally coded as polymorphic for unknown reasons, when in fact there do not seem to be any Xinpusaurus specimens with pointed posterior teeth. That the frontal remains widely separate from the external naris, so that nasal and prefrontal meet in Xinpusaurus, the plesiomorphic condition of Liu and Rieppel’s character 7, is refuted by their own description and skull reconstruction and the coding for Xinpusaurus in their matrix seems to be a typographic error. Of course Xinpusaurus shows the derived condition, as it is indicated in all existing descriptions. Liu and Rieppel (2001) also claim by their character coding that the anteromedial frontal processes are shorter than the anterolateral ones in Xinpusaurus (their character 9). In fact the reverse is the case, and they even indicate this in their description (Liu and Rieppel, 2001:80) and skull reconstruction (Liu and Rieppel, 2001:fig. 2A), probably another typographic error. At any rate the anteromedial processes of the frontals extend almost to the middle of the external naris in their specimen. The same is seen in the specimen described by Liu (2001), as well as in the material studied by Luo and Yu (2002). In fact, the so-called plesiomorphic state (which might well be an autapomorphy) is only shown by Thalattosaurus within the Thalattosauria, as correctly coded by Rieppel et al. (2000), but incorrectly by Liu and Rieppel (2001), and the value of this character is highly doubtful. Xinpusaurus also must be coded for the most derived states for Rieppel and Liu’s characters 10 and 11, as it has welldeveloped and extensive posterolateral processes of the frontals, which extend not only well beyond the anterior margins of the infratemporal fenestrae, but also contact the supratemporals, as shown not only in X. kohi but, as confirmed by our observations, also in the specimens described by Liu and Rieppel (2001) and Liu (2001). Luo and You’s (2002) skull reconstruction is mistaken in this point. For their character 16—position of the foramen parietale—

Liu and Rieppel (2001) coded Xinpusaurus with a question mark, as they could not identify the position of the parietal foramen in their specimen with confidence. As demonstrated by X. kohi as well as the material studied by Luo and Yu (2002), the parietal foramen has a posterior position in Xinpusaurus, which must therefore be coded for the plesiomorphic state. Apart from the changes enumerated above, character codings for the other thalattosaur genera were taken from Liu and Rieppel (2001) for characters 1–17 of the present analysis, which correspond to characters 1–3 and 5–18 of Liu and Rieppel (2001). The newly added characters include: (18) Lacrimal present (0) or absent (1) (modified from Nicholls, 1999). A separately ossified lacrimal is only present in Askeptosaurus italicus within thalattosaurs (Kuhn-Schnyder, 1952, 1971). It is clearly absent in Anshunsaurus (Rieppel et al., 2000), Clarazia and Hescheleria (Rieppel, 1987), Thalattosaurus and Nectosaurus (Nicholls, 1999) and Xinpusaurus (Liu and Rieppel, 2001; Luo and Yu, 2002; this study). (19) Anterior narial margin formed by premaxilla (0) or largely or exclusively by the nasal (1). In Askeptosaurus, Anshunsaurus, Hescheleria, and Clarazia (Kuhn-Schnyder, 1952, 1971; Rieppel, 1987; Rieppel et al., 2000) the anterior margin of the external naris is formed largely or exclusively by the premaxilla; the nasal has no extension anterior to the external narial opening curving around the anterior margin. Such an extension is exclusively present in Thalattosaurus (Nicholls, 1999) and Xinpusaurus (Luo and Yu, 2002; this study) within known thalattosaurs. The situation is unclear in Nectosaurus, due to incomplete preservation. (20) Prefrontal without (0) or with (1) shield-like extension along the anterodorsal orbital margin. The lateral margin of the prefrontal is smooth in Askeptosaurus (Kuhn-Schnyder, 1952, 1971), Anshunsaurus (Rieppel et al., 2000) and, apparently, Clarazia and Hescheleria (Rieppel, 1987). In the North American genera Thalattosaurus and Nectosaurus (Merriam, 1905; Nicholls, 1999) and in Xinpusaurus (Liu and Rieppel, 2001; this study), the prefrontal forms a lateral projection of shieldlike shape, similar to those found in some basal Triassic ichthyosaurs (Maisch and Matzke, 2000). This projection is rather small in Thalattosaurus but extensive in Nectosaurus and Xinpusaurus. (21) Premaxilla does not or slightly (0) or does extend far beyond the anterior narial margin (1). In Askeptosaurus and Anshunsaurus there is no or only a very slight posteroventral process of the premaxilla that does not extend far posteriorly below the external nares (Kuhn-Schnyder, 1952, 1971; Rieppel et al., 2000). In Thalattosaurus and Nectosaurus, and particularly in Xinpusaurus, such a process is clearly present (Nicholls, 1999; this study). The situation remains unclear in Clarazia, but the process is apparently present in Hescheleria (Rieppel, 1987). (22) Postnarial process of the maxilla short (0) or extensive (1). In Askeptosaurus and Anshunsaurus there is almost no noteworthy postnarial process of the maxilla. In Thalattosaurus, Hescheleria, Nectosaurus and Xinpusaurus the postnarial process is an extensive narrow spur of bone, which meets the frontal at least in Xinpusaurus and Thalattosaurus (Merriam, 1905; Rieppel, 1987; Nicholls, 1999; Liu and Rieppel, 2001; Luo and Yu, 2002; this study). The situation in Clarazia remains unclear. (23) Lower temporal fenestra extensive, of much larger size than orbit (0) or of similar size to orbit (1). The only known thalattosaur with a very extensive lower temporal fenestra is Askeptosaurus italicus (Kuhn-Schnyder, 1952, 1971). In all other known taxa included in the analysis, the temporal fenestra is only marginally larger than the orbit. (24) Surangular and angular equally well exposed on the lateral side of lower jaw (0) or surangular exposure much more

JIANG ET AL.—NEW THALATTOSAUR FROM CHINA extensive (1). In the slender mandible of Askeptosaurus, the surangular remains a rather narrow element and the angular is widely exposed (Kuhn-Schnyder, 1952, 1971). In Clarazia, the lower jaw is much shorter and rather massive; however, the angular is still an extensive element that makes up a considerable portion of the lateral mandibular surface (Rieppel, 1987). In Thalattosaurus and Nectosaurus (Merriam, 1905; Nicholls, 1999), as well as in Xinpusaurus (Liu and Rieppel, 2001; Luo and Yu, 2002; this study) the exposure of the angular is very small and more or less restricted to the ventral margin of the mandible, whereas the surangular has increased in size considerably. The lower jaw remains unknown in Anshunsaurus and only the medial side of the lower jaw is known in Hescheleria (Rieppel, 1987). (25) Supratemporal ends anteriorly behind squamosal (0) or supratemporal extends further anteriorly (1). In the basal thalattosaurs Askeptosaurus and Anshunsaurus (Kuhn-Schnyder, 1952, 1971; Rieppel et al., 2000) the supratemporal is rather short, whereas the squamosal extends considerably farther anteriorly. In the derived taxa Clarazia (Rieppel, 1987), Thalattosaurus (Nicholls, 1999), and Xinpusaurus (this study) the reverse is the case, and the supratemporal extends farther anteriorly than the reduced squamosal. The situation is unclear in Nectosaurus (Nicholls, 1999) as the squamosal is incompletely preserved in the known specimens, as well as in Hescheleria (Rieppel, 1987). (26) Scapula with convex anterior margin (0) or with concave anterior margin (1). The anterior margin of the scapula is clearly convex in Askeptosaurus (Kuhn-Schnyder, 1952) Hescheleria and Clarazia (Rieppel, 1987). It is clearly concave in Thalattosaurus (Merriam, 1905; Nicholls, 1999) and Xinpusaurus (Liu, 2001; this study). The latter state is considered as derived, in analogy to the evolution of the scapular blade in Triassic ichthyosaurs (Maisch and Matzke, 2000). (27) Thoracal neural spines short (0) or long and slender (1). The neural spines of the thoracal vertebrae are short and rectangular in Askeptosaurus (Kuhn-Schnyder, 1952), Hescheleria (Peyer, 1936b), and Clarazia (Peyer, 1936a). They are elongated, slender, and narrow in Thalattosaurus (Merriam, 1905; Nicholls, 1999), Nectosaurus (Nicholls, 1999), and Xinpusaurus (Yin et al., 2000; Liu, 2001; this study). (28) Radius concave (0) or convex anteriorly (1). The radius has a clearly concave anterior margin in Askeptosaurus (KuhnSchnyder, 1952), Hescheleria, and Clarazia (Peyer, 1936a, b; Rieppel, 1987). It is distinctly convex in Nectosaurus (Nicholls, 1999) and Xinpusaurus (Yin et al., 2000; Liu, 2001; this study). In Thalattosaurus the elements interpreted as ulnae by Merriam (1905) agree almost perfectly with the radius morphology of Xinpusaurus, as noted by Liu (2001), and we follow his suggestion to interpret this element as the radius of Thalattosaurus. (29) Femur proximal and distal ends about equal in width (0) or distal end markedly widened (1). The ends of the femur are of comparable width in Askeptosaurus (Kuhn-Schnyder, 1952). Already in Hescheleria and Clarazia (Rieppel, 1987), and much more clearly in Xinpusaurus (Liu, 2001; this study) and Thalattosaurus (Nicholls, 1999), the distal end of the femur is considerably expanded and markedly wider than the proximal end. (30) Coracoid foramen present (0) or absent (1) (from Nicholls, 1999, where the coding of this character is, however, unintelligible). Only Askeptosaurus italicus retains a coracoid foramen among known thalattosaurs (Kuhn-Schnyder, 1952). In Hescheleria and Clarazia (Rieppel, 1987), as well as in Thalattosaurus (Merriam, 1905) and Xinpusaurus, the foramen is clearly absent. The situation is unknown in Nectosaurus. If this extended data matrix is subjected to parsimony analysis, it yields three most-parsimonious trees with a length of 44 steps, a consistency index of 0.7727, and a retention index of

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FIGURE 4. Strict consensus of three most-parsimonious trees depicting the phylogenetic relationships of the well-known thalattosaur genera. Tree length is 44 steps, CI 5 0.77, RI 5 0.77.

0.7674; the strict consensus is shown in Figure 4. The indices are better than those yielded by the original analysis of Liu and Rieppel (2001), emphasizing that the new phylogeny can be considered more robust. The increase in tree length (44 versus 29 steps) is easily explicable by the addition of 13 new characters. The sister-group relationship of Xinpusaurus and Nectosaurus indicated by the results of the original analysis is further supported, as are the positions of Anshunsaurus and Askeptosaurus at the base of the Thalattosauria. As in Liu and Rieppel’s (2001) analysis, but contra Rieppel et al. (2000), the two basal genera do not form a monophyletic Askeptosauridae. Thalattosaurus is found to be the sister group of the NectosaurusXinpusaurus clade. The only significant difference to Liu and Rieppel’s (2001) cladogram is the position of Clarazia and Hescheleria, which form an unresolved trichotomy with the group of Thalattosaurus and (Xinpusaurus 1 Nectosaurus), referred to below as the ‘‘Thalattosaurus-clade.’’ In the individual mostparsimonious trees, there either is a monophyletic group consisting of Clarazia and Hescheleria as sister group of the Thalattosaurus-clade, or else one of Clarazia or Hescheleria is the immediate sister group of the Thalattosaurus-clade, with the other genus being further removed. This result has the advantage that it places the Middle Triassic Clarazia and Hescheleria rather at the base of the derived thalattosaurs, whereas the Carnian forms are found to form a monophyletic assemblage. It is therefore in better accordance with the fossil record of the thalattosaurs than the original result of Liu and Rieppel (2001). It also indicates that Xinpusaurus has closer relationships to the Carnian forms from North America than to any of the European taxa. However, as there are no Upper Triassic thalattosaurs from Europe known so far, this must not be regarded as of high paleobiogeographical significance. The addition of mandibular and postcranial characters to the data set of Liu and Rieppel (2001) which was exclusively based on cranial characters and features of the dentition, also under-

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lines the robustness of the present analysis, which takes more aspects of thalattosaur anatomy into account. Nevertheless, much remains to be learned about the osteology of thalattosaurs. As a re-study of Askeptosaurus was recently done by J. Mu¨ller (University of Mainz, Germany) and will be published soon, and as the postcranial skeleton of Anshunsaurus is under preparation (Liu, J., pers. comm.) a lot of new data will be added in the near future to our knowledge of basal thalattosaur anatomy. The derived thalattosaurs remain much more incompletely known, however, with only a single, moderately wellpreserved specimen each of the European genera Clarazia and Hescheleria and only incomplete cranial and postcranial specimens for the North American genera Thalattosaurus, Agkistrognathus, Paralonectes, and Nectosaurus available. This underlines the major importance of the newly discovered Xinpusaurus specimens from the Guanling fauna, which represent the best material by far of derived thalattosaurs presently known. ACKNOWLEDGMENTS Our sincere thanks go to Dr. Liu Jun (Institute of Vertebrate Paleontology and Paleoanthropology, Beijing), Prof. Wang YanGeng, Prof. Wang Li-Ting, and Prof. Yin Ghonzheng (Geological Survey of Guizhou, Guiyang) for assistance, discussion, and access to specimens. Dr. Winand Brinkmann (Zu¨rich) made the Monte San Giorgio thalattosaurs available for study. This study was financially supported by the DFG, NSFC, and Peking University. We thank W. Gerber, Tu¨bingen, for his assistance with the photographs. LITERATURE CITED Kuhn-Schnyder, E. 1952. Die Triasfauna der Tessiner Kalkalpen. XVII. Askeptosaurus italicus Nopcsa. Schweizerische Pala¨ontologische Abhandlungen 69:1–73. ¨ ber einen Scha¨del von Askeptosaurus italiKuhn-Schnyder, E. 1971. U cus Nopcsa aus der mittleren Trias des Monte San Giorgio. Abhandlungen des hessischen Landesamtes fu¨r Bodenforschung 60: 89–98. Liu, J. 1999. New discovery of sauropterygian from Triassic of Guizhou, China. Chinese Science Bulletin 44:1312–1315.

Liu, J. 2001. Postcranial skeleton of Xinpusaurus; pp. 1–7 in T. Deng and Y. Wang (eds.), Proceedings of the Eighth Annual Meeting of the Chinese Society of Vertebrate Palaeontology. China Ocean Press, Beijing. Liu, J., and O. Rieppel. 2001. The second thalattosaur from the Triasic of Guizhou, China. Vertebrata PalAsiatica 39:77–87. Luo, Y. M., and Y. Y. Yu. 2002. The restudy on the skull and mandible of Xinpusaurus suni. Guizhou Geology 19:71–76. Maisch, M. W., and A. T. Matzke. 2000. The Ichthyosauria. Stuttgarter Beitra¨ge zur Naturkunde, Serie B 298:1–159. Merriam, J. C. 1905. The Thalattosauria, a group of marine reptiles from the Triassic of California. Memoirs of the California Academy of Sciences 5:1–38. Merriam, J. C. 1908. Notes on the osteology of the thalattosaurian genus Nectosaurus. University of California Department of Geology Bulletin 5:217–223. Nicholls, E. L. 1999. A reexamination of Thalattosaurus and Nectosaurus and the relationships of the Thalattosauria (Reptilia, Diapsida). Paleobios 19:1–29. Nicholls, E. L., and D. B. Brinkman. 1993. New thalattosaurs (Reptilia: Diapsida) from the Triassic Sulphur Mountain Formation of Wapiti Lake, British Columbia. Journal of Paleontology 67:263–278. Peyer, B. 1936a. Die Triasfauna der Tessiner Kalkalpen. X. Clarazia schinzi nov. gen. nov. sp. Schweizerische pala¨ontologische Abhandlungen 57:1–61. Peyer, B. 1936b. Die Triasfauna der Tessiner Kalkalpen. XI. Hescheleria ruebeli nov. gen. nov. sp. Schweizerische Pala¨ontologische Abhandlungen 58:1–48. Renesto, S. 1992. The anatomy and relationships of Endennasaurus acutirostris (Reptilia, Neodiapsida), from the Norian (Late Triassic) of Lombardy. Rivista Italiana di Paleontologia e Stratigrafia 97: 409–430. Rieppel, O. 1987. Clarazia and Hescheleria, a re-investigation of two problematic reptiles from the Middle Triassic of Monte San Giorgio, Switzerland. Palaeontographica A 195:101–129. Rieppel, O., J. Liu, and H. Bucher. 2000. The first record of a thalattosaur reptile from the Late Triassic of Southern China (Guizhou Province, PR China). Journal of Vertebrate Paleontology 20:507– 514. Yin, G.-Z., X.-G. Zhuo, Z.-T. Cao, Y.-Y. Yu, and Y.-M. Luo. 2000. A preliminary study on the early Late Triassic marine reptiles from Gunanling, Guizhou, China. Geology, Geochemistry 28(3):1–22. Received 2 May 2002; accepted 8 May 2003.