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Panzhousaurus Rotundirostris Jiang et al., 2019 (Diapsida: ) and the Recovery of the of Pachypleurosauridae

Wen-Bin Lin, Da-Yong Jiang, Olivier Rieppel, Ryosuke Motani, Andrea Tintori, Zuo-Yu Sun & Min Zhou

To cite this article: Wen-Bin Lin, Da-Yong Jiang, Olivier Rieppel, Ryosuke Motani, Andrea Tintori, Zuo-Yu Sun & Min Zhou (2021): Panzhousaurus￿Rotundirostris Jiang et al., 2019 (Diapsida: Sauropterygia) and the Recovery of the Monophyly of Pachypleurosauridae, Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2021.1901730 To link to this article: https://doi.org/10.1080/02724634.2021.1901730

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Published online: 16 Apr 2021.

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Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=ujvp20 Journal of Vertebrate Paleontology e1901730 (12 pages) © by the Society of Vertebrate Paleontology DOI: 10.1080/02724634.2021.1901730

ARTICLE

PANZHOUSAURUS ROTUNDIROSTRIS JIANG ET AL., 2019 (DIAPSIDA: SAUROPTERYGIA) AND THE RECOVERY OF THE MONOPHYLY OF PACHYPLEUROSAURIDAE

WEN-BIN LIN, 1,2,3* DA-YONG JIANG,2* OLIVIER RIEPPEL,4 RYOSUKE MOTANI,5 ANDREA TINTORI,6 ZUO-YU SUN,2 and MIN ZHOU2 1School of Civil Engineering, Fujian University of Technology, Fuzhou 350118, People’s Republic of , [email protected]; 2Laboratory of Orogenic Belt and Crustal Evolution, Ministry of Education, and Department of Geology and Geological Museum, Peking University, Beijing 100871, People’s Republic of China, [email protected]; 3State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, CAS), Nanjing 210008, People’s Republic of China; 4Center of Integrative Research, The Field Museum, Chicago, IL 60605-2496, U.S.A., orieppel@fieldmuseum.org; 5Department of Earth and Planetary Sciences, University of California, Davis, CA 95616-8605, U.S.A., [email protected]; 6Dipartimento di Scienze della Terra ‘A. Desio’, Università degli Studi di Milano, Via Mangiagalli 34-20133 Milano, , [email protected]

ABSTRACT—Panzhousaurus rotundirostris Jiang, Lin, Rieppel, Motani and Sun, 2019, is restudied on the basis of a second specimen from the Upper Member of the near Panzhou City, Guizhou Province, China. The second specimen offers hitherto unknown or unconfirmed information regarding the dermal palate, the ventral aspect of the , and the hind limbs, thus permitting a refinement of the diagnosis. Newly added or modified diagnostic characters include paired frontals with no posterolateral process, elongated and slender phalanges in the and , and a phalangeal formula of 3-4-5-4-3 for the manus, and 2-3-4-5-3 for the pes. A new phylogenetic analysis of Eosauropterygia demonstrates that Pachypleurosauridae is the sister taxon of Eusauropterygia, and the monophyly of these groups as traditionally upheld is confirmed. Panzhousaurus is most closely related to Dianopachysaurus and within Pachypleurosauridae. In this study, the monophyletic excludes and . The latter two genera are found to form a monophyletic that represents the -most members of Eusauropterygia, which is in accordance with their stratigraphic distribution.

SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

Citation for this article: Wen-Bin, L., D.-Y. Jiang, O. Rieppel, R. Motani, A. Tintori, Z.-Y. Sun, and M. Zhou. 2021. Panzhousaurus rotundirostris Jiang et al., 2019 (Diapsida: Sauropterygia) and the recovery of the monophyly of Pachypleurosauridae. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2021.1901730

INTRODUCTION following the description of new genera and . Except for Placodontiformes, however, the analyses of sauropterygian inter- Sauropterygia is a monophyletic clade of secondarily relationships have yielded incongruent results, especially with adapted to aquatic life that ranged from the Early to regards to the monophyly and ingroup relationships of Pachy- the Late (Sues, 1987; Rieppel and Hagdorn, 1997; pleurosauridae and Eusauropterygia, which were supported or Rieppel,1999, 2000; Rieppel et al., 2002; Jiang et al., 2014). Trias- rejected by different analyses. The incongruent results of these sic Sauropterygia is composed of two major groups: Placodonti- analyses were probably caused by the application of different formes and Eosauropterygia, the latter comprising character scorings by various authors, but based mainly on the , , and pistosaurs (Rieppel, 2000). same data matrix taken from Rieppel (1999) and Rieppel et al. Recently, abundant Triassic sauropterygians have been (2002). The latter two analyses were based almost exclusively reported from Europe (Dalla Vecchia, 2006; Klein and Albers, on European material. Since we have recovered plenty of 2009; Neenan et al., 2013; Klein and Scheyer, 2014; Renesto eastern (Chinese mainly) specimens in the last two decades, it et al., 2014; Miguel Chaves et al., 2018a; Hinz et al., 2019) and is time to reexamine the phylogeny of the entire group, or at southwestern China (Benton et al., 2013; Jiang et al., 2014, least of the eosauropterygians, in order to assess whether and 2019; Liu et al., 2014; Ma et al., 2015; Shang and Li, 2015; how the newly described taxa affect overall tree topology. Wang et al., 2019; Li and Liu, 2020), which greatly improved Panzhousaurus rotundirostris Jiang, Lin, Rieppel, Motani our understanding of the diversity, as well as the stratigraphic and Sun, 2019, is a recently described eosauropterygian (sensu and paleogeographic distributions, of Triassic sauropterygians. Rieppel, 1994) from the middle () The phylogeny of Sauropterygia was also repeatedly analyzed Guanling Formation in Guizhou Province, China. It is charac- terized by the combination of the following features: rounded and shortened snout, relatively long with 24 cervical ver- tebrae, four distal carpals, and elongated, slender phalanges in * Corresponding authors. Color versions of one or more of the figures in the article can be found the manus and pes (Jiang et al., 2019). The holotype and until online at www.tandfonline.com/ujvp. recently the only known specimen of Panzhousaurus provides

Published online 16 Apr 2021 Lin et al.—Second specimen of Panzhousaurus rotundirostris (e1901730-2) no information on the ventral aspect of the and the ver- primarily on the data matrix of Lin et al. (2019), which is a com- tebrae. Here, we describe a second specimen of this taxon bination of phylogenetically informative characters for resolving from the same locality and same stratigraphic level as the holo- the interrelationships of Eosauropterygia and its subgroups such type. The specimen was briefly described by Lin et al. (2019), as pachypleurosaurs and nothosaurs. but incomplete preparation at the time obscured many osteolo- Character Selection—We used 148 morphological characters, gical features. The specimen described here not only reveals the of which 37 from Lin et al. (2019) and 11 from Li and Liu ventral view of the skull, but also variation in the postcranial (2020) were not used in previous research (e.g., Rieppel et al., skeleton, which results in a revised diagnosis of the species. In 2002; Liu et al., 2011; Neenan et al., 2013; Shang et al., 2017; addition, we conduct a phylogenetic analysis to test the inter- Jiang et al., 2019). This then greatly expanded the data matrix relationships of Eosauropterygia. for analyzing the relationships of eosauropterygians. The deri- vation and definition of characters are given in Supplemental Data 1. Character scores were carefully checked and several MATERIALS AND METHODS scoring errors were corrected (see Appendix S1 in Supplemental The specimen (GMPKU-P-3241; Figs. 1–4) described herein Data 1). was collected during the 2006 field season from Bed 87 of the Ingroup Selection—Bobosaurus forojuliensis (Dalla Vecchia, Upper Member of the Guanling Formation at Dapianpo 2006), cristatus (Hinz et al., 2019) and Quarry in Yangjuan Village, Xinmin Town, Panzhou City (for- sanxiaensis (Li and Liu, 2020) were added to the ingroup of merly Panxian County), Guizhou Province (Motani et al., 2008; Lin et al. (2019), whereas Nothosaurus zhangi was excluded Jiang et al., 2009). It was prepared by mechanical tools under a from the analysis because in this taxon only 16 of the 148 charac- microscope. Measurements were collected using digital calipers ters could be coded. Paludidraco multidentatus (Miguel Chaves with a precision of 0.02 mm, and are provided in Table 1. et al., 2018a) was not included because the original description GMPKU-P-3241 is quite well preserved (Fig. 1), lacking only was brief and incomplete, and we did not study the specimen some elements of the pectoral girdle and the forelimbs. The first hand. We also excluded Dawazisaurus brevis (Cheng et al., whole skeleton is preserved on three separate slabs, produced 2016) because it was never diagnosed properly to distinguish it during the excavation: one displaying the skull, the neck, the from Dianopachysaurus dingi. Its postulated vertebral count, anterior part of the dorsal , the pectoral which is supposed to be diagnostic of the , cannot be girdle, and a (Fig. 1A); the second slab comprises the confirmed because of a crack. Therefore, nearly all currently posterior part of the dorsal vertebral column, the sacral vertebral recognized Triassic eosauropterygian genera were included column, the pelvic girdle, the right hind limb, and the tail (Fig. in the analysis, resulting in a total of 45 ingroup taxa. In the cla- 1A); the third slab displays the left hind limb in ventral view distic analysis of Rieppel et al. (2002), the European pachypleur- (Fig. 1B). Some elements of the specimen, especially the pectoral osaurs , , Dactylosaurus and girdle and the humerus, have been dislocated anteriorly. were combined and coded into two terminal Given that the ingroup relationships of Placodontiformes are ‘taxa’ (e.g., Neustico-Serpiano and Anaro-Dactylo), which were well established, as is its position as the basal-most clade of Saur- adopted by most later analyses, but they are coded separately opterygia, we herein focus on reanalyzing the interrelationships herein. Compared with previous global analyses, Nothosaurus of Eosauropterygia, which is the sister clade of the Placodonti- and Lariosaurus were coded at the species level to test the mono- formes within the Sauropterygia. To reexamine the phylogeny phyly of each genus. This then is the most inclusive phylogenetic of the Eosauropterygia, we conducted a cladistic analysis based analysis of the Eosauropterygia to date.

FIGURE 1. A new specimen of Panzhousaurus rotundirostris (GMPKU-P-3241) from the middle Anisian (Middle Triassic) Panxian Fauna. A, the whole skeleton; B, left hind limb in ventral view. Lin et al.—Second specimen of Panzhousaurus rotundirostris (e1901730-3)

FIGURE 2. Skull of Panzhousaurus rotundirostris (GMPKU-P-3241) in ventral view (modified after Lin et al., 2019). A, photograph; B, interpretive drawing. Abbreviations: a, angular; bo, basioccipital; cn, coronoid; d,dentary;ec,ectopterygoid; eo, exoccipital; f,frontal;in,internalnaris;m, ; n,nasal;p, parietal; pa, palatine; pf, postfrontal; prar, prearticular; pt,pterygoid; q, quadrate; sa, surangular; sq, squamosal. Scale bar equals 5 mm.

Outgroup Selection—Based on several recent phylogenetic Definition—A monophyletic clade including the most recent analyses of sauropterygians and saurosphargids, placodonts common ancestor of Hanosaurus hupehensis and Neusticosaurus have consistently been found to be the immediate sister group edwardsii, and all its descendants. of eosauropterygians (Neenan et al., 2013, 2015; Klein and Emended Diagnosis (Modified after Rieppel, 2000, and Liu Scheyer, 2014; Li et al., 2014; Jiang et al., 2019). Therefore, et al., 2011)—Small- to medium-sized eosauropterygian with we selected four traditional and well-studied placodonts (i.e., relatively short snout; preorbital region of skull distinctly , , Cymodus, ) as outgroups longer than postorbital region; lateral edge of frontal concave; for the analysis of interrelationships of Eosauropterygia. The upper temporal fossa smaller than orbit; trough on dorsal position of the Eosauropterygia or Sauropterygia within the surface of retroarticular process present; vertebral centrum Amniota is beyond the scope of the current study. with parallel lateral edges; pachyostosis of dorsal ribs present Analysis—Mesquite 2.74 (Maddison and Maddison, 2010) (convergent in Lariosaurus); last dorsal rib longer than first was used for constructing the character matrix (Supplemental sacral rib; posterior process on (T-shaped) interclavicles rudi- Data 1). Multistate characters were treated as unordered, and mentary or absent; dorsal iliac blade reduced to simple dorsal all characters were equally weighted. The data matrix was ana- process; longer than . lyzed using both TNT 1.1 (Goloboff et al., 2008)andPAUP version 4.0a 168 for 32-bit Microsoft Windows (Swofford, Panzhousaurus rotundirostris Jiang, Lin, Rieppel, Motani and 2020). The four placodont outgroups were constrained as Sun, 2019 monophyletic before the phylogenetic analysis. A heuristic (Figs. 1–4) search was used in PAUP by running 1000 replicates of random addition sequences and TBR branch swapping, Holotype—GMPKU-P-1059, an almost complete skeleton. holding 100 trees at a time. New technology searches were per- Referred Specimen—GMPKU-P-3241, a nearly complete formed in TNT at level 10, with 100 hits, 100 replications, 10 skeleton lacking some elements of the pectoral girdle and of drifts, holding 10 trees per replicate, and using rule-3 collapse. the forelimbs. The TNT search was followed by bootstrap analysis (based on Locality and Horizon—Pelsonian, Middle Anisian, Middle 10,000 replicates) and Bremer support estimation. The strict Triassic, Upper Member of Guanling Formation (Yang et al., consensus tree was computed in TNT, as shown in Figure 5. 1999; Sun, 2006; Liu, 2015); Dapianpo Quarry, Yangjuan The Bremer support analysis included trees that are within 10 Village, Xinmin Town, Panzhou City, Guizhou Province, China. steps of the shortest trees. Emended Diagnosis (Modified after Jiang et al., 2019)— Institutional Abbreviations—GMPKU, Geological Museum Small-sized with distinctly short, broad, and of Peking University, Beijing, People’s Republic of China. rounded rostrum (autapomorphy among Pachypleurosauridae); postorbital region of skull distinctly longer than preorbital region; upper temporal fenestra elongated but only about half SYSTEMATIC PALEONTOLOGY the longitudinal diameter of orbit; prefrontal small; paired fron- Superorder SAUROPTERYGIA Owen, 1860 tals with no posterolateral process, meeting nasals anteriorly at Order EOSAUROPTERYGIA Rieppel, 1994 level of anterior margin of orbit (autapomorphy among Pachy- Suborder PACHYPLEUROSAURIA Nopcsa, 1928 pleurosauridae); 24 cervical, 20 dorsal, and three sacral vertebrae Family PACHYPLEUROSAURIDAE Nopcsa, 1928 (autapomorphy among Eosauropterygia); cervical region shorter Lin et al.—Second specimen of Panzhousaurus rotundirostris (e1901730-4)

FIGURE 3. Selected regions of Panzhousaurus rotundirostris. A, B, atlas-axis region of GMPKU-P-3241 in ventral view; C, cervical rib of GMPKU-P- 3241 in dorsal view; D, E, pectoral girdle and pelvic girdle of GMPKU-P-3241 in dorsal view; F, G, dorsal vertebrae and ribs of GMPKU-P-3241 in dorsal view; H, dorsal ribs of the holotype (GMPKU-P-1059). Abbreviations: at, atlas; ati, atlas intercentrum; atr, atlas rib; ax, axis; axa, axis arch; axr, axis rib; cl, ; co, ; cof, coracoid foramen; cr, caudal rib; cvr, cervical rib; dr, darsal rib; ecg, ectepicondylar groove; enf, entepicon- dylar foramen; gr, groove; hu, humerus; il, ; is, ischium; pu, ; r, rib; sc, ; sr, sacral rib; v, .

than the trunk region; radius as long as ulna, but thinner; ulna phalanges in manus and pes; phalangeal formula 3-4-5-4-3 straight, with concave anterior and posterior margins; six for manus, and 2-3-4-5-3 for pes (autapomorphy among carpal and four tarsal ossifications; elongated and slender Pachypleurosauridae). Lin et al.—Second specimen of Panzhousaurus rotundirostris (e1901730-5)

FIGURE 4. Lower part of the hind limbs of Panzhousaurus rotundirostris. A, right hind limb of the holotype (GMPKU-P-1059) in dorsal view; B, left hind limb of the referred specimen (GMPKU-P-3241) in ventral view; C, right hind limb of the referred specimen (GMPKU-P-3241) in dorsal view. Abbreviations: as, astragalus; ca, calcaneum; dt, distal tarsal; fi, fibula; mt, metatarsal; ti, . Scale bars equal 5 mm.

BRIEF DESCRIPTION comparison. Therefore, in the following description we will focus primarily on the structures not yet described, or unavailable The skeleton of specimen GMPKU-P-3241 as a whole is well to Jiang et al. (2019) and Lin et al. (2019), as well as on the com- articulated. The anterior part of the specimen is exposed in parison with other pachypleurosaurs and nothosaurs. ventral view, whereas the rest is twisted and exposed in dorsal view (Fig. 1). The preserved length of the skeleton is 220 mm. The preserved portion of the skull is 14.43 mm in length (from Skull the anterior end of the incompletely preserved snout to the pos- terior margin of the occipital condyle). The standard length (the The skull itself is incomplete, as the anterior portion of the snout last four dorsal vertebrae) is 13.23 mm, and the preserved 22 could not be recovered during the excavation (Fig. 2), and in caudals are in total 75 mm in length. The referred specimen is addition was dorsoventrally compressed, resulting in some break- smaller than the holotype, the former being about 53.7% in age. Although the skull is preserved in ventral view, some dorsal humerus length, 55.4% in length, and about 60.2% in stan- elements can be identified. This is because the pterygoids have dard length of the latter. The skull, pectoral and pelvic girdles, and been separated along the midline, probably as a result of tapho- hind limbs of the specimen GMPKU-P-3241 were briefly nomic deformation during preservation, thus exposing the ventral described and figured in a Chinese monograph (Lin et al., 2019), surface of the nasal, the frontal, the postfrontal, and the parietal. and GMPKU-P-3241 was tentatively referred to Panzhousaurus, The paired frontals are narrow in the referred specimen as is but it is now identified as a referred specimen of Panzhousaurus also the case in the holotype and in Dianmeisaurus gracilis rotundirostris after detailed preparation and taxonomic (Shang and Li, 2015)(Fig. 2). The anterior process of the Lin et al.—Second specimen of Panzhousaurus rotundirostris (e1901730-6)

TABLE 1. Measurements (in mm) of the new specimen of lie entirely in front of the disarticulated humerus, and are here Panzhousaurus rotundirostris (GMPKU-P-3241). interpreted as cervicals (Figs. 1, 3D). The 19th and the anterior half of the 20th vertebrae are covered by the humerus and Length of preserved postcranial skeleton 205.57 their corresponding ribs are missing (Fig. 3D). Posterior to the Length of atlas centrum 1.00 20th vertebra, the vertebral column is twisted from a ventral to Length of axis centrum 1.82 Length of the last dorsal rib 8.10 a dorsal exposure in the area of the pectoral girdle (Fig. 3D, Length of the first sacral rib 6.50 F). Eighteen complete dorsal vertebrae and an incomplete one Length of left humerus 15.84 (the 27th vertebra), which is crushed because of the split of the Proximal width of left humerus 3.11 slab during excavation, are preserved (Fig. 3D). Specimen Minimal width of left humerus 2.50 GMPKU-P-3241 thus has minimally 39 presacral vertebrae, but Distal width of left humerus 4.86 due to the overlapping humerus and the disarticulated ribs, the Length of right femur 15.50 – Proximal width of right femur 3.65 exact location of the cervical dorsal boundary cannot be ident- Minimal width of right femur 1.34 ified. Furthermore, some vertebrae might have been lost during Distal width of right femur 2.08 the excavation, such that the exact number of presacral vertebrae Length of right tibia 6.94 in the referred specimen is impossible to determine, whereas it is Proximal width of right tibia 1.61 discernible in the holotype with a total of 44 presacrals. There- Minimal width of right tibia 1.87 fore, there might have been five additional presacrals in the Distal width of right tibia 2.11 Length of right fibula 7.05 referred specimen. There are three sacral vertebrae, and 22 Proximal width of right fibula 1.03 caudal vertebrae preserved (Figs. 1, 3E). Minimal width of right fibula 1.23 The elements of the atlas-axis complex are obscured in the Distal width of right fibula 1.81 holotype due to poor preservation, but they are discernible in Length of left metatarsal I 2.69 the referred specimen (Fig. 3A, B). The atlantal centrum is Length of left metatarsal II 4.93 Length of left metatarsal III 5.80 short, being only about half the length of the axis (Table 1), Length of left metatarsal IV 5.80 and not fused with the latter. It is spherical, with a concavity Length of left metatarsal V 4.31 on its anterior surface. A small bone is present in front of the Length of first phalange of digit 1 of the pes 1.36 atlas (Fig. 3A, B). It might be the atlas intercentrum, which is Length of first phalange of digit 2 of the pes 1.17 also present in Neusticosaurus edwardsii (Carroll and Gaskill, Length of first phalange of digit 3 of the pes 2.93 fi fi 1985: g. 13d) and Serpianosaurus mirigiolensis (Rieppel, 1989: Length of rst phalange of digit 4 of the pes 3.01 fi Length of first phalange of digit 5 of the pes 92.84 g. 5a). The axial centrum has essentially the same shape as that of the rest of the cervical vertebrae, and it is only slightly shorter than the following centrum. However, its anterolateral margin shows a peculiar shelf for the articulation of the proximal head of the axis rib (Fig. 3A, B). The axis neural arch bears a frontal is distinctly present, which is obscured in the type speci- postzygapophyseal process articulating with the 3rd vertebra. men due to damage. Posterolaterally, the frontal forms a nearly The atlantal ribs are well preserved; they are roughly triangular straight suture with the postfrontal. Different from other small elements, broader and shorter than the remaining cervical ribs. pachypleurosaurs, the posterolateral process of the frontal is The axis rib is slender, and shorter than the 4th cervical rib. absent as in the holotype (Jiang et al., 2019). Anterior to the The cervical ribs are double-headed, with a free anterior pineal foramen, the parietals are sutured, whereas they are process, as shown by two disarticulated cervical ribs, one fully fused in the larger holotype, which may indicate ontogenetic located on the left side of the 14th vertebra (Figs. 1, 3C), and variation in Panzhousaurus. another one located in front of the scapula (Fig. 3D). Most elements of the palate are preserved, except for the There are no noticeable differences in the morphology of the vomers (Fig. 2). The right internal naris is partially preserved remaining postcranial skeletons between the two specimens. fi except for its anterior margin. It is de ned by the maxilla laterally The surface of the dorsal ribs is generally smooth in the referred and bordered by the palatine posteriorly. The right palatine is specimen (Fig. 3F, G), whereas a shallow and slender posterior better preserved and more completely exposed than the left groove is present on the proximal shoulder region of the dorsal one, which was partially lost during preservation. Posterior to ribs in the posterior trunk of the holotype (Fig. 3H). There are the internal naris, the palatine meets the maxilla in a curved seven more caudal vertebrae, but two or three fewer caudal suture. Judging from the medial margin of the palatine, the pala- ribs in GMPKU-P-3241, which can be attributed to preservation. tine-pterygoid suture is weakly interdigitating. Posteriorly, the Three tarsal ossifications are present in the pes (Fig. 4B, C), palatine extends to contact the ectopterygoid along a concave including the kidney-shaped astragalus, the rounded calcaneum, suture. The pterygoids have separated from each other along and distal tarsal IV, which is also present in the holotype (Fig. the midline. Laterally, the pterygoid forms a weakly developed 4A) and in some adult specimens of Keichousaurus (Rieppel transverse process, which together with the ectopterygoid com- and Lin, 1995; Jiang et al., 2019). Distal tarsal III is also fl poses the transverse pterygoid ange. Posteromedially, the ptery- present in the holotype (Fig. 4A), which makes for a total of goids meet in an interdigitating suture. A crack is present in the four tarsal ossifications, as specified in the diagnosis above. The posterior middle part of the pterygoids due to damage. Poster- metatarsals are more slender than in the type specimen (Fig. 4). iorly, they form a broad plate of bone, extending back to the occi- The phalanges are slender, elongate and constricted medially pital condyle, and thus covering all of the endocranial basicranium (Fig. 4B, C). Except for digit 2, the length of first phalanges in ventral view. The ectopterygoids are preserved on both sides, equals or exceeds 50% of the length of the corresponding meta- fl forming the greater part of the transverse pterygoid ange. Medi- tarsals in the pes, as is also the case in the holotype (Table 1; ally, they meet the pterygoids in a slightly convex suture. Poster- Fig. 4A). The unguals of first four digits are expanded; they are iorly, the ectopterygoid tapers to a narrow projection. larger than the penultimate phalanx, as is also the case in the holotype, as well as in Dianopachysaurus, Diandongosaurus, and Dianmeisaurus (Liu et al., 2011; Shang et al., 2011, 2017; Postcranium Shang and Li, 2015; Jiang et al., 2019). The fifth digit lacks an The vertebrae are preserved in articulation; only the distal tip expanded claw, which is also not present in the aforementioned of the tail is missing. Eighteen vertebrae exposed in ventral view species (Sato et al., 2014a; Liu et al., 2015; pers. observ.), Lin et al.—Second specimen of Panzhousaurus rotundirostris (e1901730-7)

FIGURE 5. Strict consensus tree of the phyloge- netic interrelationships among Eosauropterygia from TNT (14 MPTs, TL = 613, CI = 0.3116, and RI = 0.6594). A, unnamed clade comprising all of the Middle Triassic pachypleurosaurs; B, unnamed clade comprising all of the Middle Triassic pachypleurosaurs except for Diandongosaurus and Dianmeisaurus; C, unnamed clade comprising Panzhousaurus, Dianopachysaurus, and Keichousaurus. D, unnamed clade comprising Dactylosaurus, Anarosaurus, Odoiporosaurus, Wumengosaurus, Qianxisaurus, Serpianosaurus,andNeusticosaurus. E,thecladeofLariosaurus. Values above branches leading to the nodes represent Bremer support, and the values below the branches are bootstrap values ≥ 50% (10,000 replicates).

suggesting that the fifth digit of those species may not have borne (GMPKU-P-1059) during the excavation at Yangjuan village, such a claw in life. Therefore, the preserved phalangeal formula and can be definitely ascribed to that species based on the com- of the pes for Panzhousaurus is 2-3-4-5-3, which is nearly com- bination of the following features: the narrow interorbital bridge; plete judging from the appearance of the distal phalanges in paired frontals with no distinct posterolateral process; length of both the referred specimen and the holotype. the humerus longer than that of the femur; the first phalanges of digits 1, 3, 4 and 5 relatively elongate and slender; and a corre- sponding phalangeal formula in the pes. However, specimen COMPARISON GMPKU-P-3241 provides some new information for the The referred specimen (GMPKU-P-3241) was found in the species concerning the ventral aspect of the skull, the braincase, same bed as the holotype of Panzhousaurus rotundirostris and the structure of the atlas-axis complex. Beyond that, it also Lin et al.—Second specimen of Panzhousaurus rotundirostris (e1901730-8) shows some features that are not present or cannot be ascer- is within the range of variation observed in other pachypleuro- tained in the holotype. The anterior process of the frontal is saurs. (3) The dorsal ribs are pachyostotic proximally as in most obviously present in the referred specimen, which is unclear in pachypleurosaurs, unlike Diandongosaurus and Dianmeisaurus,in the type specimen due to damage. Anterior to the parietal which the dorsal ribs are not pachyostotic. (4) The humerus is foramen, the parietals are unfused in the referred specimen. slightly longer than the femur, unlike those pachypleurosaurs from The frontoparietal suture is deeply embayed (concave) in the the Luoping Biota, such as Dinopachyosaurus, Diandongosaurus, holotype, but is interdigitating in the referred specimen. With and Dianmeisaurus, in which the humerus is distinctly shorter respect to the postcranial skeleton, a longitudinal groove is than the femur. (5) The radius and ulna are straight and present on the proximodorsal surface of the dorsal ribs in the of almost the same length, similar to Dinopachyosaurus and posterior trunk of the holotype, unlike in the referred specimen, Dianmeisaurus, but different from Diandongosaurus, where the surface of the dorsal ribs is generally smooth. Further- Keichousaurus, and European pachypleurosaurs, in which the more, there are four tarsal ossifications present in the holotype, radius is longer than the ulna. (6) Six carpal ossifications are but only three in the referred specimen. These differences are evident in the left manus of the holotype of Panzhousaurus, possibly due to intraspecific or ontogenetic variation as in which is the highest number among well-known pachypleuro- other eosauropterygians (Sander, 1989; Lin and Rieppel, 1998; saurs, a plesiomorphic character. There are only two or three Rieppel, 2000; Shang and Li, 2015; Shang et al., 2017; Li and carpal ossifications in other pachypleurosaurs, except for Liu, 2020). Keichousaurus, which has five carpals. (7) Four tarsal ossifications Information derived from the second specimen allows us to are present in the holotype of Panzhousaurus, which is again the better distinguish Panzhousaurus rotundirostris from other highest number among known pachypleurosaurs, comparable only Chinese small-sized pachypleurosaurs, which have a slender to Anarosaurus heterodontus (Klein, 2012). (8) The phalanges in and short body (less than 50 cm in length), a skull with a rela- the digits of manus and pes of Panzhousaurus are distinctly tively large orbit, a small upper temporal fenestra, and an elongate and slender, whereas they are relatively short and stout elongate neck and tail (Shang et al., 2017). To date, five small- in Dianopachysaurus, Diandongosaurus,andDianmeisaurus sized pachypleurosaur species have been described from the (Liu et al., 2011; Shang et al., 2011;ShangandLi,2015). The Middle Triassic of China (Young, 1958; Liu et al., 2011; Shang unguals of the second to fourth digits are distinctly enlarged, et al., 2011; Shang and Li, 2015; Jiang et al., 2019), among which is the same as in Chinese Anisian pachypleurosaurs, such which Dianopachyosaurus dingi, Diandongosaurus acutidentatus, as Dianopachysaurus, Diandongosaurus,andDianmeisaurus,but and Dianmeisaurus gracilis are all from the Anisian (Middle has never been reported in other pachypleurosaurs. (9) The pha- Triassic) Luoping Biota, whereas only Panzhousaurus is known langeal formula of the manus is 3-4-5-4-3, and the phalangeal from the time-equivalent Panxian Fauna. Keichousaurus hui is formula of the pes is 2-3-4-5-3, which are both different from from the late (Middle Triassic) Xingyi Fauna. those of any other pachypleurosaurs. With respect to the skull elements, the following features need to be emphasized. (1) The rostrum in Panzhousaurus is extre- PHYLOGENETIC ANALYSIS mely short and broadly rounded, unlike in other pachypleuro- saurs in which the rostrum is also short but tapers to an Rieppel (1999, 2000) and Rieppel et al. (2002) gave compre- anterior blunt tip. (2) The bridge between the external naris hensive reviews of research on the interrelationships of those and the orbit is very narrow, which is different from most other sauropterygians described by the end of the last century. Since pachypleurosaurs, but comparable to the condition seen in then, as more taxa were reported, especially from the Triassic Dianmeisaurus (Shang and Li, 2015). (3) The prefrontal is of South China, our knowledge of the diversity of sauroptery- rather small, located at the anterodorsal corner of the orbit, gians has been greatly enriched. Meanwhile, many phylogenetic unlike in all other pachypleurosaurs. (4) The postorbital region analyses of sauropterygians have been presented by various of the skull is distinctly longer than the preorbital region, researchers, usually in combination with the description of a which is similar to that of some of pachypleurosaurs, such as new taxon or re-description of a named taxon (e.g., Cheng Keichousaurus, Dianopachysaurus, and Dianmeisaurus (Lin and et al., 2006, 2012; Holmes et al., 2008; Jiang et al., 2008, 2014, Rieppel, 1998; Liu et al., 2011; Shang and Li, 2015). This 2019; Sato et al., 2014a, b; Liu et al., 2011; Shang et al., 2011, feature is also seen in most nothosaurs (Rieppel, 2000). (5) The 2017; Wu et al., 2011; Neenan et al., 2013; Klein and Scheyer, upper temporal fenestra is less than half the longitudinal diam- 2014; Ma et al., 2015; Miguel Chaves et al., 2018b), but all eter of the orbit in Panzhousaurus, whereas the ratio of the longi- data matrices were mostly based on and/or originated from tudinal diameter of upper temporal fenestra to that of the orbit is those of Rieppel (1999) and Rieppel et al. (2002). Although between 0.5–1.0 in other Chinese small-sized pachypleurosaurs the monophyly and deep phylogenetic relationships of the Saur- (Holmes et al., 2008; Liu et al., 2011; Shang et al., 2011; Shang opterygia have not changed, the interrelationships of the and Li, 2015). Eosauropterygia have been incongruent between different ana- Regarding features of the postcranial skeleton, the following lyses, especially regarding the monophyly of Pachypleurosauri- structures or areas need to be mentioned. (1) The atlas intercen- dae and Eusauropterygia. The results of most cladistic trum is evident in the referred specimen of Panzhousaurus. analyses showed that Pachypleurosauridae as traditionally con- This is comparable to Neusticosaurus edwardsii (Carroll and ceived is not a monophyletic clade, and the Chinese pachypleur- Gaskill, 1985:fig. 13d) and Serpianosaurus mirigiolensis osaur-like forms were found to be more closely related to the (Rieppel, 1989:fig. 5a). In contrast, the axis intercentrum is Nothosauroidea than to the European pachypleurosaurs (e.g., present in Neusticosaurus pusillus (Sander, 1989:fig. 14) and Holmes et al., 2008; Cheng et al., 2012; Sato et al., 2014a; Dianmeisaurus (Shang and Li, 2015). (2) There are 44 presacral Shang et al., 2011, 2017; Wu et al., 2011). In contrast, the mono- vertebrae (24 cervicals and 20 dorsals) in the holotype of phyly of Pachypleurosauridae was supported by some other Panzhousaurus; the elongated presacral portion of the body is analyses, in which the Chinese forms were considered to be different from that of other pachypleurosaurs, in which there closely related to the European pachypleurosaurs, and the are fewer than 40 presacrals (Rieppel, 2000). The number Nothosauroidea was found to be the sister group of the Pachy- of cervical vertebrae in Panzhousaurus is close to that of pleurosauridae (Neenan et al., 2013; Klein and Scheyer, 2014;Li Keichousaurus, which has 25 or 26 cervicals (Rieppel and Lin, and Liu, 2020), or grouped with the Pistosauroidea to form the 1995), but higher than in most other pachypleurosaurs Eusauropterygia (sensu Rieppel, 2000) in accordance with the (Rieppel, 2000). The count of dorsal vertebrae in Panzhousaurus historical view (Jiang et al., 2008; Liu et al., 2011; Renesto Lin et al.—Second specimen of Panzhousaurus rotundirostris (e1901730-9) et al., 2014; Lin et al., 2019). Following the discovery of the than to nothosaurs as was also the case in some recent cladistic second specimen of Panzhousaurus, and detailed observations analyses, which focused on resolving the phylogenetic inter- and comparisons of all relevant species of Eosauropterygia, relationships of Nothosaurus and Lariosaurus (Liu et al., 2014; the phylogenetic interrelationships of the Eosauropterygia, Klein et al., 2016; Lin et al., 2017; Hinz et al., 2019). These and the monophyly of the Pachypleurosauridae and Eusaurop- three species group together with the species of Lariosaurus to terygia were reexamined in this study. form the monophyletic clade E (Fig. 5), though the interrelation- We present here a cladistic analysis of a data matrix comprising ships of the clade are unresolved, which might be the result of a 148 characters for 49 taxa (see Materials and Methods, and significant amount of missing data for L. sanxiaensis. Other Supplemental Data 1), based on a revision of the data matrix species of Nothosaurus are excluded from this clade, but do not of Lin et al. (2019), which differed from the most recent phyloge- form a monophyletic clade of their own. As far as the monophyly netic analysis of eosauropterygians by Li and Liu (2020) mainly of Pistosauroidea is concerned, Wangosaurus is found to be the by the inclusion of more ingroup taxa but fewer characters. We most basal member of that clade, as was also the case in previous used four placodonts as outgroup taxa, whereas Li and Liu research (Ma et al., 2015; Jiang et al. 2019;Linetal.,2019), and is (2020) employed three non-sauropterygian and one the sister taxon to the ((Augustasarus, )(, sauropterygian (i.e., Placodus) as outgroups. Therefore, the (Bobosaurus, ))) clade. interpretation of character evolution in our analysis and that of In addition, we also conducted a phylogenetic analysis by Li and Liu (2020) is different. adding Panzhousaurus to the data matrix of Li and Liu (2020), In our phylogenetic analysis, the heuristic search in PAUP found while combining 17 characters of Lin et al. (2019) and one char- 18 most parsimonious trees (MPTs; tree length [TL] = 613 steps, acter of Rieppel and Lin (1995) with those of Li and Liu (2020) consistency index [CI] = 0.3116, retention index [RI] = 0.6594), of (see Supplemental Data 2 for more details). The result indicates which 14 were also found by a new technology search in TNT. that Panzhousaurus is a member of Pachypleurosauridae, as The strict consensus tree shows that Panzhousaurus rotundirostris was also the case in our phylogenetic analysis, but it is more is a member of Pachypleurosauridae (Fig. 5). Four major closely related to the four European pachypleurosaurs (Sup- of Triassic eosauropterygians are robustly supported as mono- plemental Data 2; Figs. 5, S1). Though Pachypleurosauridae, phyletic, including Pachypleurosauridae, Cymatosauridae, Nothosauroidea, and Pistosauroidea are found to be monophy- Nothosauroidea, and Pistosauroidea. The ingroup topologies of letic, neither the relationships of these three clades, nor the Pachypleurosauridae, Cymatosauridae, and Pistosauroidea are internal relationships of Pachypleurosauridae and Nothosauroi- resolved, whereas the taxa included in the Nothosauroidea dea clades are resolved (Fig. S1). Although the data matrix remain unresolved to a certain degree. Nothosaurus winkelhorsti, of Li and Liu (2020) contains more characters than the Nothosaurus juvenilis, L. sanxiaensis, L. hongguoensis, present matrix, many are autapomorphic or phylogenetically L. vosseveldensis, and L. buzzii form a polytomy. uninformative (Supplemental Data 2). Their data are already The strict consensus tree of our analysis indicates that the Early reflected in our matrix through the addition of 11 of their charac- Triassic eosauropterygians Hanosaurus and Majiashanosaurus are ters that are not redundant to the present matrix. The discussion the most basal taxa of Pachypleurosauridae (Fig. 5). They form suc- below is based on the more fully resolved tree topology obtained cessive outgroups of the clade (clade A) that comprises all of the by our phylogenetic analysis (Fig. 5), which contains more Middle Triassic pachypleurosaurs. The sister-taxa Diandongosaurus eosauropterygians compared with the data matrix of Li and and Dianmeisaurus occupy a basal position in this clade, and Liu (2020). form the sister group of clade B consisting of two monophyletic clades (clade C and clade D). Within clade C, Panzhousaurus is DISCUSSION found to be the sister taxon of a clade comprising Dianopachysaurus and Keichousaurus, which is similar to the result of Lin et al. The strict consensus tree of our analysis recovers the monophyly (2019), but is in striking contrast to the results presented by of the Pachypleurosauridae as historically conceived, and the Jiang et al. (2019). In contrast to previous analyses, the four Euro- Chinese taxa Hanosaurus and Majiashanosaurus pean pachypleurosaurs do not form a monophyletic clade, but are are the most basal members of this clade, a topology which grouped together with two Chinese taxa, Wumengosaurus and accords well with their early appearance in the geological Qianxisaurus, and the European pachypleurosaur Odoiporosaurus record. The monophyly of Pachypleurosauridae is supported by to form the monophyletic clade D (Fig. 5). The monophyly of Pachy- the following four unequivocal synapomorphies: character 5(0), pleurosauridae is also supported by Li and Liu (2020). However, in snout relatively short; character 21(0), lateral edge of frontal the of Li and Liu (2020), Pachypleurosauridae rather concave; character 37(2), ratio of longitudinal diameter of constitutes the sister group of Nothosauroidea to form an upper temporal fossa to that of orbit less than 1.0; and character unnamed clade, Majiashanosaurus and Hanosaurus form succes- 92(1), pachyostosis of dorsal ribs present. The monophyly of sive outgroups of this clade instead of nesting within the Pachy- Pachypleurosauridae has been controversial in the past, whereas pleurosauridae, and the four European pachypleurosaur genera it is independently recovered in this study, as well as in the two form a monophyletic clade. most recent phylogenetic analyses of sauropterygian interrelation- Regarding the monophyly of Eusauropterygia, Corosaurus ships offered by Lin et al., (2019) and Li and Liu (2020). This may and Cymatosaurus form the monophyletic clade Cymatosauridae be the result of the discovery in recent of new pachypleuro- (sensu Huene, 1944), exclusive of the Nothosauroidea and Pisto- saurs and nothosaurs, and of better-preserved specimens of forms sauroidea, and represent the most basal clade of Eusauropterygia previously known only from fragmentary material, which allow a (Fig. 5), which differs from all previous analyses (except for Lin comprehensive revision of the of the relevant species. et al., 2019), where the two taxa are either more closely related It may also possibly be attributed to the significant improvement to pistosauroids or, alternatively, to nothosauroids. The ingroup of the data matrix. Compared with the data matrix of Rieppel topology of Nothosauroidea is generally identical to traditional et al. (2002) and most of the later studies, a number of new char- phylogenetic analyses, e.g., ( (Germanosaurus, acters were added to the current data matrix, which is based on the )). However, within the Nothosauridae clade, data matrix of Lin et al. (2019), and also on that of Li and our result corroborates the collapse of the monophyly of the Liu (2020), concomitant with the critical revision of several orig- genera Nothosaurus and Lariosaurus as traditionally defined. inal characters and codings. In addition, the four European Nothosaurus youngi, Nothosaurus juvenilis, and Nothosaurus pachypleurosaur genera and the species of Nothosaurus and winkelhorsti are found to be more closely related to lariosaurs Lariosaurus have been coded separately in our data matrix and Lin et al.—Second specimen of Panzhousaurus rotundirostris (e1901730-10) in that of Li and Liu (2020), whereas the four European pachy- the current analysis (Fig. 5), the results presented here require pleurosaur genera were combined and coded into two terminal future corroboration. More informative characters, new com- ‘taxa’ and Nothosaurus and Lariosaurus were coded at the plete specimens and re-description of historical material, are genus level in previous research. required to improve the analysis of sauropterygian phylogenetic Our analyses found that the sister-taxa Corosaurus and interrelationships in the future. Cymatosaurus were outside the clade including Nothosauroidea and Pistosauroidea because they lacked a set of unambiguous synapomorphies of that clade, such as the ratio of the longitudi- nal diameter of upper temporal fossa to that of the orbit exceed- ACKNOWLEDGMENTS ing 2.0, broad medially, the dorsal wing or process of the eosauropterygian scapula tapering to a blunt tip, and the inter- L. Schmitz, A. Boyd, S. Hinic-Frlog, and J.-Y. Shin joined the fi trochanteric fossa being rudimentary or absent. The phylogenetic eld trip and excavation in 2006 and helped with the collection positions of those two taxa as shown in our analysis is in accord- of the specimen here described. We thank C. Li and Q.-H. ance with their early stratigraphic occurrence. Corosaurus is Shang (IVPP), S.-X. Hu (CCCGS), L.-J. Zhao (ZMNH), from the latest (Early Triassic) Alcova , C. Klug (PIMUZ), G. Teruzzi (MCSNM), T. Schossleitner Wyoming, U.S.A. (Storrs, 1991; Rieppel, 1998; Lovelace and (MNF-Berlin), E. Maxwell (SMNS), C. Ifrim (PGIMUH), Doebbert, 2015), which is the earliest occurrence of a eusaurop- J. M. Rabold (UMO-Bayreuth) and P. Vincent (MNHN) for terygian . Cymatosaurus first appears in the fossil record in providing access to the specimens under their care. W.-B. Lin the uppermost Buntsandstein (earliest Anisian, Middle Triassic) especially thanks T. M. Scheyer for his help at PIMUZ. This of Rüdersdorf near Berlin, (Huene, 1944; Rieppel, research was supported by Projects 41920104001, 40920124002, 2000; Maisch, 2014). Hence, it is older than the first occurrence and 41372016 from the National Natural Science Foundation of Nothosauroidea in the lower Gogolin Beds (lower Muschelk- of China, Grant 2016YFC0503301 from the Ministry of alk, early Anisian, Middle Triassic) of Upper Silesia, Poland Science and Technology, Project 2020J05183 from the Natural (Rieppel and Wild, 1996), and the first occurrence of Pistosauroi- Science Foundation of Fujian Province, Project 203112 from dea in the upper (upper Anisian, Middle Triassic) of State Key Laboratory of Palaeobiology and Stratigraphy Bayreuth, Germany (Sues, 1987), or in the Fossil Hill Member of (Nanjing Institute of Geology and Palaeontology, CAS), and the Favret Formation (upper Anisian, Middle Triassic) of Projects GY-Z18146 and GY-Z20091 from Fujian University Nevada, U.S.A. (Sander et al., 1997). of Technology. We also acknowledge the grant from the Our cladistic analysis indicates that Nothosauridae is a mono- National Geographic Society Committee for Research and phyletic clade, whereas the monophyly of the included genera Exploration (#8669-09) to R. Motani. W.-B. Lin was supported Lariosaurus and Nothosaurus is not supported. Such inter- by a grant from Peking University for three months of research relationships of Nothosauridae differ dramatically from previous in . global phylogenetic analyses, but has been suggested in the phy- logenetic analyses of Nothosauridae. As pointed out by Klein et al. (2016), Lin et al. (2017, 2019), and Hinz et al. (2019), ORCID fi based on morphological and phylogenetic af nities, Nothosaurus Wen-Bin Lin http://orcid.org/0000-0002-0887-1420 juvenilis, Nothosaurus youngi, and Nothosaurus winkelhorsti should be referred to the genus Lariosaurus,asL. juvenilis, L. youngi, and L. winkelhorsti, respectively. In that way, the monophyly of the genus Lariosaurus is re-established. It is diag- LITERATURE CITED nosed by three unambiguous characters including external nares Benton, M. J., Q.-Y. Zhang, S.-X. Hu, Z.-Q. Chen, W. Wen, J. Liu, J.-Y. retracted, narrow, and with a longitudinal diameter distinctly less Huang, C.-Y. Zhou, T. Xie, J.-N. Tong, and B. Choo. 2013. than half the longitudinal diameter of orbit, nasal-prefrontal Exceptional vertebrate biotas from the Triassic of China, and the expansion of marine ecosystems after the Permo-Triassic mass contact present, and the ratio of longitudinal diameters of – upper temporal fossa to orbit between 1.0 and 2.0. . Earth Science Reviews 125:199 243. Carroll, R. L., and P.Gaskill. 1985. The Pachypleurosaurus and Compared with some of the previous research, Pistosauroidea the origin of plesiosaurs. Philosophical Transactions of the Royal is limited to include Wangosaurus, Pistosaurus, , Society of London B 309:343–93. Yunguisaurus, Bobosaurus, and Plesiosaurus and all of its descen- Cheng, Y.-N., T. Sato, X.-C. Wu, and C. Li. 2006. Fist complete pistosaur- dants, as was recovered in the analysis of Ma et al. (2015) and Lin oid from the Triassic of China. Journal of Vertebrate Paleontology et al. (2019). This group was supported by the following charac- 26:501–504. ters: 30(1), jugal entering upper temporal arch; 38(2), the antero- Cheng, Y.-N., X.-C. Wu, T. Sato, and H.-Y. Shan. 2012. A new eosaurop- medial corner of upper temporal fossa fully floored by a terygian (Diapsida, Sauropterygia) from the Triassic of China. – descensus from postorbital, which together with neighboring Journal of Vertebrate Paleontology 32:1335 1349. elements (postfrontal, parietal) separates it from the orbit; 134 Cheng, Y.-N., X.-C. Wu, T. Sato, and H.-Y. Shan. 2016. Dawazisaurus fi brevis, a new eosauropterygian from the Middle Triassic of (0), total number of tarsal ossi cations four or more. , China. Acta Geologica Sinica (English Edition) 90:401– In summary, Panzhousaurus is a small-sized pachypleurosaur, 424. and closely related to Dianopachysaurus and Keichousaurus.The Dalla Vecchia, F. M. 2006. A new sauropterygian with plesiosaur- global parsimony analysis of Triassic Eosauropterygia conducted ian affinity from the of Italy. Rivista Italiana di here confirms the monophyly of the clades Pachypleurosauridae Paleontologia e Stratigrafia, 112:207–225. and Eusauropterygia. Phylogenetic analysis also supports the Goloboff, P. A., J. S. Farris, and K. C. Nixon. 2008. TNT, a free program monophyly of Lariosaurus, whereas Nothosaurus as previously for phylogenetic analysis. 24:774–786. conceived is not monophyletic. One major difference between Hinz, J. K., A. T. Matzke, and H.-U. Pfretzschner. 2019. A new nothosaur the current study and previous research is the position of the (Sauropterygia) from the Ladinian of Vellberg-Eschenau, southern Germany. Journal of Vertebrate Paleontology. doi: 10.1080/ sister taxa Corosaurus and Cymatosaurus. They are the most 02724634.2019.1585364. basal members of Eusauropterygia, which accords well with Holmes, R., Y.-N. Cheng, and X.-C. Wu. 2008. New information on the their early stratigraphic occurrence. However, because the boot- skull of Keichousaurus hui (Reptilia: Sauropterygia) with comments strap values (10,000 replications) of the data matrix (Supplemen- on sauropterygian interrelationships. Journal of Vertebrate tal Data 1) as well as the Bremer support (decay index) are low in Paleontology 28:76–84. Lin et al.—Second specimen of Panzhousaurus rotundirostris (e1901730-11)

Huene, F. V. 1944. Ein beachtenswerter Humerus aus dem untersten Xingyi level, southwestern China. Journal of Muschelkalk und seine Bedeutung. Neues Jahrbuch für Geologie Vertebrate Paleontology 35: e881832. und Paläontologie, Monatshefte, Abteilung B 1944:223–227. Maddison, W. P., and D. R. Maddison. 2010. Mesquite: a modular system Jiang, D.-Y., W.-B. Lin, O. Rieppel, R. Motani and Z.-Y. Sun. 2019. A new for evolutionary analysis, version 2.74. Available at http:// Anisian (Middle Triassic) eosauropterygian (Reptilia, mesquiteproject.org. Sauropterygia) from Panzhou, Guizhou Province, China. Journal Maisch, M. W. 2014. A well preserved skull of Cymatosaurus (Reptilia: of Vertebrate Paleontology 38: e1480113. Sauropterygia) from the uppermost Buntsandstein (Middle Jiang, D.-Y., O. Rieppel, R. Motani, W.-C. Hao, Y.-L. Sun, L. Schmitz, Triassic) of Germany. Neues Jahrbuch für Geologie und and Z.-Y. Sun. 2008. A new middle Triassic eosauropterygian Paläontologie, Monatshefte 2014:213–224. (Reptilia, Sauropterygia) from southwestern China. Journal of Miguel Chaves, C. de, F. Ortega, and A. Pérez-García. 2018a. New highly Vertebrate Paleontology 28:1055–1062. pachyostotic nothosauroid interpreted as a filter-feeding Triassic Jiang, D.-Y., R. Motani, W.-C. Hao, O. Rieppel, Y.-L. Sun, A. Tintori, marine reptile. Biology Letters 14:20180130. doi: 10.1098/rsbl. Z.-Y. Sun, and L. Schmitz. 2009. Biodiversity and sequence of the 2018.0130 Middle Triassic Panxian marine reptile fauna, Guizhou Province, Miguel Chaves, C. de, F. Ortega, and A, Pérez-García. 2018b. Cranial varia- China. Acta Geologica Sinica (English Edition) 81:451–459. bility of the European Middle Triassic sauropterygian Simosaurus gail- Jiang, D.-Y., R. Motani, A. Tintori, O. Rieppel, G.-B. Chen, J.-D. Huang, lardoti. Acta Palaeontologica Polonica 63:315–326. R. Zhang, Z.-Y. Sun, and C. Ji. 2014. The Early Triassic eosauropter- Motani, R., D.-Y. Jiang, A. Tintori, Y.-L. Sun, W.-C. Hao, A. Boyd, S. ygian Majiashanosaurus discocoracoidis, gen. et sp. nov. (Reptilia, Hinic-Frlog, L. Schmitz, J.-Y. Shin, and Z.-Y. Sun. 2008. Horizons Sauropterygia), from Chaohu, Anhui Province, People’s Republic and assemblages of Middle Triassic marine reptiles from Panxian, of China. Journal of Vertebrate Paleontology 34:1044–1052. Guizhou, China. Journal of Vertebrate Paleontology 28:900–903. Klein, N. 2012. Postcranial morphology and growth of the pachypleuro- Neenan, J. M., N. Klein, and T. M. Scheyer. 2013 . European origin of pla- saur Anarosaurus heterodontus (Sauropterygia) from the Lower codont marine reptiles and the evolution of crushing dentition in Muschelkalk of Winterswijk, The . Paläontologische . Nature Communications 4:1621. doi: 10.1038/ Zeitschrift 86:389–408. ncomms2633. Klein, N., and P.C. H. Albers. 2009. A new species of the sauropsid reptile Neenan, J. M., C. Li, O. Rieppel and T. M. Scheyer 2015. The cranial Nothosaurus from the Lower Muschelkalk of the western Germanic anatomy of Chinese placodonts and the phylogeny of Placodontia Basin, Winterswijk, The Netherlands. Acta Palaeontologica (Diapsida: Sauropterygia). Zoological Journal of the Linnean Polonica 54:589–598. Society 175:415–428. Klein, N., and T. M. Scheyer. 2014. A new placodont sauropterygian from Nopcsa, F. 1928. Palaeontological notes on reptiles. Geologica the Middle Triassic of the Netherlands. Acta Palaeontologica Hungarica, Series Palaeontologica 1:3–84. Polonica 59:887–902. Owen, R. 1860. Palaeontology; or, a Systematic Summary of Extinct Klein, N., D. F. A. E. Voeten, A. Haarhuis, and R. Bleeker. 2016. The ear- and Their Geologic Remains. Adam and Charles Black, liest record of the genus Lariosaurus from the early middle Anisian Edinburgh, xv + 420 pp. (Middle Triassic) of the Germanic Basin. Journal of Vertebrate Renesto, S., G. Binelli, and H. Hagdorn. 2014. A new pachypleurosaur Paleontology. doi: 10.1080/02724634.2016.1163712. from the Middle Triassic of Northern Italy. Li, C., D.-Y. Jiang, L. Cheng, X.-C. Wu, and O. Rieppel. 2014. A new Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen species of Largocephalosaurus (Diapsida: Saurosphargidae), with 271:151–68. implications for the morphological diversity and phylogeny of the Rieppel, O. 1989. A new pachypleurosaur (Reptilia: Sauropterygia) from group. Geological Magazine 151:100-120. the Middle Triassic of Monte San Giorgio, Switzerland. Li, Q., and J. Liu. 2020. An Early Triassic sauropterygian and associated Philosophical Transactions of the Royal Society of London B fauna from South China provide insights into Triassic ecosystem 323:1–73. health. Communications Biology 3:63. doi: 10.1038/s42003-020-0778-7. Rieppel, O. 1994. Osteology of Simosaurus gaillardoti, and the phyloge- Lin, K.-B., and O. Rieppel. 1998. Functional morphology and ontogeny of netic interrelationships of stem group Sauropterygia. Fieldiana Keichousaurus hui (Reptilia, Sauropterygia). Fieldiana Geology Geology 28:1–85. 39:1–35. Rieppel, O. 1998. Corosaurus alcovensis Case and the phylogenetic inter- Lin, W.-B., D.-Y. Jiang, O. Rieppel, R. Motani, C. Ji, A. Tintori, Z.-Y. Sun, relationships of Triassic stem-group Sauropterygia. Zoological and M. Zhou. 2017 . A new specimen of Lariosaurus xingyiensis Journal of the Linnean Society 124:1–41. (Reptilia, Sauropterygia) from the Ladinian (Middle Triassic) Rieppel, O. 1999. The sauropterygian genera Chinchenia, Kwangsisaurus Zhuganpo Member, Falang Formation, Guizhou, China. Journal and Sanchiaosaurus from the Lower and Middle Triassic of China. of Vertebrate Paleontology 37: e1278703. Journal of Vertebrate Paleontology 19:321–337. Lin, W.-B., M. Zhou, and D.-Y. Jiang. 2019. Systematic study of the Rieppel, O. 2000. Sauropterygia I: Placodontia, Pachypleurosauria, eosauropterygians from the Triassic of South China. Science Press, Nothosauroidea, Pistosauroidea. Encyclopedia of Paleoherpetology, Beijing, China, 154pp. [Chinese] Volume 12A. Verlag Dr. Friedrich Pfeil, Munich, 134pp. Liu, J. 2015. Discussion of ‘The Triassic U–Pb age for the aquatic long- Rieppel, O., and H. Hagdorn. 1997. Paleobiogeography of Middle necked protorosaur of Guizhou, China’. Geological Magazine Triassic Sauropterygia in Central and Western Europe; pp. 121– 152:572–573. 144 in J. M. Callaway and E. L. Nicholls (eds.), Ancient Marine Liu, J., O. Rieppel, D.-Y. Jiang, J. C. Aitchison, R. Motani, Q.-Y. Zhang, Reptiles. Academic Press, San Diego. C.-Y. Zhou, and Y.-Y. Sun. 2011. A new pachypleurosaur (Reptilia: Rieppel, O., and K.-B. Lin. 1995. Pachypleurosaurs (Reptilia: Sauropterygia) from the lower Middle Triassic of southwestern Sauropterygia) from the Lower Muschelkalk, and a review of the China and the phylogenetic relationships of Chinese pachypleuro- Pachypleurosauroidea. Fieldiana Geology 32:1–44. saurs. Journal of Vertebrate Paleontology 31:291–302. Rieppel, O., and R. Wild. 1996. A revision of the genus Nothosaurus Liu, J., S.-X. Hu, O. Rieppel, D.-Y. Jiang, M. Benton, N. Kelley, J. (Reptilia, Sauropterygia) from the Germanic Triassic, with com- Aitchison, C.-Y. Zhou, W. Wen, J.-Y. Huang, T. Xie, and T. Lv. ments on the status of Conchiosaurus clavatus. Fieldiana Geology 2014. A gigantic nothosaur (Reptilia: Sauropterygia) from the 34:1–82. Middle Triassic of SW China and its implication for the Triassic Rieppel, O., P. M. Sander, and G. W. Storrs. 2002. The skull of the pisto- biotic recovery. Scientific Reports 4:7142. doi: 10.1038/srep07142. saur Augustasaurus from the Middle Triassic of northwestern Liu, X.-Q., W.-B. Lin, O. Rieppel, Z.-Y., Sun, Z.-G. Li, H. Lu, and D.-Y. Nevada. Journal of Vertebrate Paleontology 22:577–592. Jiang. 2015. A new specimen of Diandongosaurus acutidentatus Sander, P. M. 1989. The pachypleurosaurids (Reptilia: Nothosauria) from (Sauropterygia) from the Middle Triassic of Yunnan, China. the Middle Triassic of Monte San Giorgio, (Switzerland), with the Vertebrata PalAsiatica 53:281–290. [Chinese] description of a new species. Philosophical Transactions of the Lovelace, D. M., and A. C. Doebbert. 2015. A new age constraint for the Royal Society of London, B 325:561–670. Early Triassic Alcova Limestone (Chugwater Group), Wyoming. Sander, P. M., O. Rieppel, and H. Bucher. 1997. A new pistosaurid Palaeogeography, Palaeoclimatology, Palaeoecology 424:1–5. (Reptilia: Sauropterygia) from the Middle Triassic of Nevada and Ma, L.-T., D.-Y. Jiang, O. Rieppel, R. Motani, and A. Tintori. 2015.A its implications for the origin of the plesiosaurs. Journal of new pistosauroid (Reptilia, Sauropterygia) from the late Ladinian Vertebrate Paleontology 17:526–533. Lin et al.—Second specimen of Panzhousaurus rotundirostris (e1901730-12)

Sato, T., Y.-N. Cheng, X.-C. Wu, and H.-Y. Shan. 2014a. Diandongosaurus Sun, Z.-Y. 2006. Studies on the Middle and Upper Triassic biostratigra- acutidentatus Shang, Wu & Li, 2011 (Diapsida: Sauropterygia) and phy in western Guizhou and eastern Yunnan, China. Ph.D. disser- the relationships of Chinese eosauropterygians. Geology tation, Peking University, Beijing, China, 110 pp. Magazine 151:121–133. Swofford, D. L. 2020. PAUP* 4.0a168. Phylogenetic Analysis Using Sato, T., L.-J. Zhao, X.-C. Wu, and C. Li. 2014b. A new specimen of Parsimony (*And Other Methods). Sinauer Associates, the Triassic pistosauroid Yunguisaurus, with implications for the Sunderland, Massachusetts. origin of (Reptilia, Sauropterygia). Paleontology Wang, W., C. Li, T. M. Scheyer, and L.-J. Zhao. 2019. A new species of 57:55–76. Cyamodus (Placodontia, Sauropterygia) from the early Late Shang, Q.-H., and C. Li. 2015. A new small-sized eosauropterygian Triassic of south-west China, Journal of Systematic Palaeontology (Diapsida: Sauropterygia) from the Middle Triassic of Luoping, 17:1457–1476. Yunnan, southwestern China. Vertebrata PalAsiatica 53:265–280. Wu, X.-C., Y.-N. Cheng, C. Li, L.-J. Zhao, and T. Sato. 2011. New [Chinese] information on Wumengosaurus delicatomandibularis Jiang et al., Shang, Q.-H., C. Li, and X.-C. Wu. 2017. New information on 2008 (Diapsida: Sauropterygia), with revision of the osteology and Dianmeisaurus gracilis Shang & Li, 2015. Vertebrata PalAsiatica phylogeny of the taxon. Journal of Vertebrate Paleontology 31:70–83. 55:145–161. Yang, S.-R., W.-C. Hao, and X.-P. Wang. 1999. Triassic conodont Shang, Q.-H., X.-C. Wu, and C. Li. 2011. A new eosauropterygian from sequences from different facies in China; pp. 97–112 in A. Yao, Y. the Middle Triassic of eastern Yunnan Province, southwestern Ezake, W.-C. Hao, and X.-P. Wang (eds.), Biotic and Geological China. Vertebrata PalAsiatica 49:155–173. Development of the Paleo-Tethys in China. Peking University Storrs, G. W. 1991. Anatomy and relationships of Corosaurus alcovensis Press, Bejing, China. (Diapsida: Sauropterygia) and the Triassic Alcova Limestone of Young, C.-C. 1958. On the new Pachypleurosauroidea from Kweichow, Wyoming. Bulletin of the Peabody Museum of Natural History southwest China. Vertebrata PalAsiatica 2:69–81. 44:1–151. Sues, H.-D. 1987. Postcranial skeleton of Pistosaurus and interrelation- Submitted April 20, 2020; revisions received December 10, 2020; ships of the Sauropterygia (Diapsida). Zoological Journal of the accepted December 14, 2020. Linnean Society 90:109–131. Handling Editor: Erin Maxwell.