From the Middle Triassic of Panxian, Guizhou, Southwestern China and Its Position in the Triassic Biotic Recovery

Home , Guanling Formation, Mixosaurus, Utatsusaurus

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Progress in Natural Science 18 (2008) 1315–1319 www.elsevier.com/locate/pnsc

Short communication New primitive ichthyosaurian (Reptilia, Diapsida) from the Middle Triassic of Panxian, Guizhou, southwestern China and its position in the Triassic biotic recovery

Dayong Jiang a,*, Ryosuke Motani b,*, Weicheng Hao a, Lars Schmitz b, Olivier Rieppel c, Yuanlin Sun a, Zuoyu Sun a

a Department of Geology and Geological Museum, Peking University, Beijing 100871, China b Department of Geology, University of California, Davis, CA 95616-8605, USA c Department of Geology, The Field Museum, Chicago, IL 60605-2496, USA

Received 16 November 2007; received in revised form 8 January 2008; accepted 10 January 2008

Abstract

A new primitive ichthyopterygian Xinminosaurus catactes gen. et. sp. nov. is erected based on a complete skeleton from the Middle Triassic Upper Member of the Guanling Formation at Panxian, Guizhou, southwestern China. It has a suite of uniquely derived char- acters in its dentition, ulna, carpals and tarsals. It is similar to primitive ichthyopterygians in retaining elongated limb bones. The new taxon and a diversity of marine reptiles in Panxian Fauna are the physical markers of the Middle Triassic Biotic radiation. Detailed studies of this fauna will supply essential knowledge on the diversity, migration and paleobiogeographic aﬃnity of Middle Triassic ichthyopterygians. Ó 2008 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved.

Keywords: Ichthyosauria; Ichthyopterygia; Middle Triassic; Panxian; Guizhou

1. Introduction shanensis from the Lower Triassic of Chaohu in Anhui [3], for which multiple skeletons are known. Recently, abun- Limited by the rare and fragmentary fossil records, only dant Triassic marine reptile fossils associated with ﬁshes, a few ichthyopterygians were reported from China before bivalves, branchiopods, echinoids and other fossils were the end of last century: Mixosaurus maotaiensis that was found in Guizhou Province, viz., Panxian Fauna in age named based on fragmentary elements of pectoral girdle of Anisian (Middle Triassic) [4–14], Xingyi Fauna in age and forelimb from the Middle Triassic of Renhuai in of Ladinian (Middle Triassic) [15–19], Guanling Biota in Guizhou [1], Himalayasaurus tibetensis based on several age of Carnian (Late Triassic) [20–27], among which the vertebrae and fragmentary elements of jaw and forelimb most attractive ones are the complete articulated and from the Upper Triassic of Tibet [2], and Chaohusaurus gei- well-preserved skeletons of ichthyosaurus, especially those from Panxian Fauna and Guanling Biota.

* Compared to Guanling Biota, Panxian Fauna is of older Corresponding authors. Tel./fax: +86 10 62754154. E-mail addresses: [email protected] (D. Jiang), motani@geology. age and also of higher biodiversity. Its appearance and ucdavis.edu (R. Motani). composition are diﬀerent from the Triassic Chaohu Fauna,

1002-0071/$ - see front matter Ó 2008 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved. doi:10.1016/j.pnsc.2008.01.039 1316 D. Jiang et al. / Progress in Natural Science 18 (2008) 1315–1319

Xingyi Fauna and Guanling Biota. The dominant ichthyosaur group in Panxian Fauna is Mixosauridae, such as Mixosaurus panxianensis and Phalarodon cf. Phalarodon fraasi [6,7,10,14], but also contains a new primitive ichthyopterygian, which is reported in this paper.

2. Systematic palaeontology

2.1. Systematic position and diagnosis of new taxon

Class Reptilia Linnaeus, 1758 Subclass Diapsida Osborn, 1903 Superorder Ichthyopterygia Owen, 1840 Order Ichthyosauria Blainville, 1835 Family incertae sedis Genus Xinminosaurus gen. nov. Xinminosaurus catactes gen. et sp. nov. Holotype: GMPKU-P-1071, a nearly complete skeleton (Figs. 1–4) deposited in Geological Museum, Peking University. Etymology: Xinmin, district where the fossil was found; saurus from Greek sauros, lizard; catactes, crusher, from Fig. 2. Skull of the holotype of Xinminosaurus catactes gen. et. sp. nov. Greek kataktes (Katagnumi), breaker. (GMPKU-P-1071). Abbreviations: d, dentary; j, jugal; m, maxilla; q, Locality and horizon: Near Yangjuan Village, Xinmin quadrate. Scale bars = 10 cm. District, Panxian County, Guizhou Province, China. Conodont Nicoraella kockeli biozone (Pelsonian, Anisian, 2.2. Comparison Middle Triassic), Upper Member, Guanling Formation. Diagnosis: An Ichthyopterygia with the following auta- Xinminosaurus catactes can be clearly identified as a pomorphies: bulbous and laterally compressed crushing member of the Ichthyopterygia by its tailbend in the middle teeth in maxilla and posterior dentary; no vertical median caudal vertebral column with the neural spines inclined constriction of tooth crown; snout tip possibly edentulous; anteriorly to form the caudal peak, and its humerus with replacement teeth outside pulp cavities, forming second the anterior blade, which are the synapomorphies of the tooth rows in maxilla and dentary; distal facet of ulna Superorder Ichthyopterygia. The number of its presacral greatly expanded, extending proximally beyond mid-shaft vertebrae reaches 60, much higher than those in the prim- region; distal carpals 3 and 4 fused; distal carpal 1 unossi- itive ichthyopterygians such as Utatsusaurus and Chaohu- fied; distal tarsals 3 and 4 fused; distal tarsal 1 unossified. saurus (about 40), but resembles those in ichthyosaurus such as Cymbospondylus and Besanosaurus [28]. This derived feature may suggest that the new genus probably is a member of Order Ichthyosauria. However, it is differ- ent from other ichthyosaurians by its forefin and hindfin retaining elongated limb bones, digits with fewer phalanges probably not exceeding five in any digit, and the shapes of metacarpals and metatarsals, which resemble those of primitive ichthyopterygians such as Utatsusaurus and Chaohusaurus [28–31]. It can be distinguished from all the other ichthyopterygians by its special dentition with crushing teeth, ulnar shape and feature of carpals and tarsals, indicating it can be erected as a new genus and new species. Its crushing dentition, however, seems generally similar to those of Tholodus schmidi, an enigmatic ichthyosaur from the Middle Triassic of Europe [32–34]. It is difficult to make detailed comparison with this taxon because T. schmidi was named on a fragmentary dentition with massive crushing teeth, and furthermore, the maximum Fig. 1. Holotype skeleton of Xinminosaurus catactes gen. et. sp. nov. (GMPKU-P-1071), from the Upper Member of Guanling Formation diameter of the crushing teeth of T. schmidi may reach (Pelsonian, Anisian, Middle Triassic) of Yangjuan Village, Xinmin 18–28 mm, which is twice as large as those in the new District, Panxian County, Guizhou Province, China. Scale bar = 20 cm. taxon. D. Jiang et al. / Progress in Natural Science 18 (2008) 1315–1319 1317

Fig. 4. Right hindlimb of the holotype of Xinminosaurus catactes gen. et. sp. nov. (GMPKU-P-1071). Abbreviations: a, astragalus; c, calcaneum; f, femur; ﬁ, ﬁbula; ti, tibia. Scale bars = 5 cm.

of the Superorder Ichthyopterygia. The new taxon clearly presents this feature (Fig. 1). The skull is broken and fragmentary (Fig. 2); the jugal, quadrate, part of maxilla and sclerotic ring can be recog- nized; the others are too fragmentary to be identified. The most distinguished feature in the skull is the bulbous and laterally compressed crushing teeth 5–13 mm in diam- Fig. 3. Left forelimb of the holotype of Xinminosaurus catactes gen. et. sp. eter in maxilla and posterior dentary, which has no vertical nov. (GMPKU-P-1071). Abbreviations: cl, clavicle; h, humerus; i, inter- median constriction of tooth crown. The teeth in the ante- medium; r, radius; ra, radiale; sc, scapula; u, ulna; ul, ulnare. Scale rior dentary are conical. The snout tip is possibly edentu- bars = 5 cm. lous, and the replacement teeth are outside of the pulp cavities of their predecessors, forming the second and med- 3. Brief description ial tooth rows in maxilla and dentary. The postcranial skeleton is almost completely articu- The skeleton is 2.32 m long, the skull is 29 cm long lated. The clavicle is short and broad. The scapular is a (along midline of palate), the dorsal trunk is 103.5 cm fan-shaped blade with glenoid process well set off from long, and the tail is 99.5 cm long. There are 140 verte- the main body, its anterior extension is slightly larger than brae, including 60 presacral, 3 sacral and 77 caudal ver- the posterior extension, and the convex distal margin con- tebrae. The caudal vertebral column presents a tains a shallow notch. The humerus is 7 cm long, and downward tailbend of 35° in the middle from the 38th 3.9 cm wide distally, no shaft constriction but bearing obvi- caudal vertebra, forming an angle of 145° with the ante- ous anterior blade, which is another synapomorphy of the rior part of the tail, and accordingly the neural spines in Superorder Ichthyopterygia [28]. The radius is 5.3 cm long, the area incline anteriorly to form the caudal peak. The 3.0 cm wide proximally, 2.4 cm distally, and 1.3 cm in shaft caudal peak in the middle caudal vertebral column with constriction, respectively. The ulna is distinguished by its the neural spines inclined anteriorly is a synapomorphy expanded distal facet that is 4.1 cm wide, which extends 1318 D. Jiang et al. / Progress in Natural Science 18 (2008) 1315–1319 proximally beyond the mid-shaft region. The ulna is 5.1 cm Spitsbergen [39,40], Chaohusaurus from Anhui of China long, with its proximal end 1.9 cm wide, and mid-shaft con- [3,30,31,41],andUtatsusaurus from Japan [29,42,43].In striction 1.7 cm wide. Three rectangular proximal carpals the Middle Triassic, along with the stabilization of the mar- are present, in which the ulnare is the largest one spanning ine paleoenvironment after the pronounced instability in 2 cm in maximum diameter. The distal carpal 2 is round the Early Triassic, rapid biotic radiation quickly estab- and 1.1 cm in diameter, whereas the distal carpal 1 is unos- lished a new ecosystem. Many new taxa evolved among sified and the distal carpals 3 and 4 are fused to become a ichthyopterygians at this time, including Mixosaurus, Pha- rectangular bone with 1.6 cm in length and 1.1 cm in width. larodon, Cymbospondylus, Besanosaurus. These forms rap- The metacarpals and phalanges retain elongated shafts idly spread across a wide geographical region, with constriction, similar to those of primitive ichthyop- encompassing the western Tethys (Germanic and Alpine terygians such as Utatsusaurus and Chaohusaurus [28–31] Basins), eastern Panthalassa (Nevada and British Colum- but not other ichthyopterygians. Of the five metacarpals, bia), and Guizhou of China [28]. While the biodiversity the 1st is the shortest at 1.3 cm (although it is broad), reached its highest in the Late Triassic, the pelagic ichthy- whereas the 3rd and 4th are the longest at 2.4 cm. The opterygians e.g. Shastasaurus and Shonisaurus evolved, 5th metacarpal is kidney shaped and 1.9 cm long, with con- along with Chinese forms such as Guizhouichthyosaurus, cave anterior margin and convex posterior margin. The Guanlingsaurus, and Himalayasaurusi [2,24,28]. morphology and arrangement of the metacarpals are simi- The overall studies on the origin and early evolution of lar to Utatsusaurus [28,29], but appear more slender. The ichthyopterygians, including their biodiversity, phyloge- preserved phalangeal formula is 3-5-5-5-2 (Fig. 3), netic relationships, paleobiogeography, and functional Of hindfin, the femur, tibia and fibula are all shorter ecology, still require scrutiny because our current under- than the corresponding forelimb bones, respectively. The standing is based on rare and fragmentary specimens from femur is 5.5 cm long, 2.6 cm wide proximally, 3.5 cm dis- a limited number of localities. Though ichthyopterygians tally, and 1.8 cm at the mid-shaft constriction, respectively. were among the top predators in the Mesozoic marine eco- The tibia is 4.5 cm long and 3.2 cm wide at the proximal system, their role during the Triassic biotic recovery has end, which is about twice as broad as the distal end of been almost completely ignored. The new findings from 1.7 cm. The fibula is 4.5 cm long, 1.5 cm wide proximally Guizhou should enable us to deepen our understanding and 3.5 cm distally. Two almost round proximal tarsals of ichthyopterygian evolution in the context of post-Perm- are present, of which the astragalus is slightly smaller than ian recovery. the calcaneum. The metatarsals and phalanges resemble the The Middle Triassic Panxian Fauna in Guizhou is the corresponding forefin elements, retaining elongated shafts. physical marker of the rapidly expanding biodiversity in The 5th metatarsal, as in the 5th metacarpal, is kidney the Middle Triassic, containing abundant well-preserved shaped. The phalangeal formula cannot be established and diversified ichthyosaur fossils. The two Mixosaurid because the phalanges are not completely preserved ichthyosaurians Mixosaurus panxianensis and Phalarodon (Fig. 4). cf. P. fraasi have already been reported [6,7,10], and we report in this paper a new ichthyosaurian, X. catactes 4. Position of Xinminosaurus and panxian fauna in the gen. et. sp. nov., which bears some derived features of triassic biotic recovery Ichthyosauria such as high count of the presacral vertebrae, while retaining plesiomorphic ichthyopterygians The end-Permian mass extinction caused great biotic features such as the elongated limb bones. Further and environmental distraction on this planet. The bio- detailed study on Panxian Fauna will expand our knowl- sphere, from its macroscopical appearance, began to edge on the biodiversity, stratigraphic distribution and slowly step into recovery in the drastically unstable envi- paleogeographic distribution of early ichthyopterygians, ronment during the Early Triassic. Then, during the and will provide important information to discuss the Middle Triassic, the organisms rapidly radiated, and evolution, the phylogeny and paleographic affinity of Tri- finally in the Late Triassic the biodiversity reached its assic ichthyosaur. Furthermore, it will add an important highest and the biodiversity completely recovered from perspective from the top predators to the study of the the mass extinction [35]. The course of this recovery Triassic Biotic Recovery, which has so far concentrated encompasses many scientific questions, such as the origin mostly on prey. of new groups, patterns of changes in biodiversity, evolution of the biota as a whole, the relationships between Acknowledgments the biotic evolution and paleoenvironmental changes, and paleogeographic changes. These hot topics are This work was supported by National Natural Science attracting much attention of paleontologists and other Foundation of China (Grant Nos. 40672002 and scientists in the world [36–38]. 40302009), Program for New Century Excellent Talents As an important group of Mesozoic marine reptiles, Ich- in University (NCET-07-0015), and the Committee for Re- thyopterygia first emerged at the end of the Early Triassic. search and Exploration of the National Geographic Soci- The early ichthyopterygians include Grippia from arctic ety (Grant 7886-05). Mr. Henrik Sto¨hr (Tu¨bingen, D. Jiang et al. / Progress in Natural Science 18 (2008) 1315–1319 1319

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