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

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From the Middle Triassic of Panxian, Guizhou, Southwestern China and Its Position in the Triassic Biotic Recovery Available online at www.sciencedirect.com 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 stud- ies 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 ichthyo- saur 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 ichthy- opterygian, 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 crush- ing 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.
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