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Article: First subadult specimen of Psephochelys polyosteoderma (Sauropterygia, Placodontia) implies turtle‐like fusion pattern of the carapace

Papers in Palaeontology - Volume 6 Issue 2 - Cover
Publication: Palaeontology
Volume: 6
Part: 2
Publication Date: May 2020
Page(s): 251 264
Author(s): Wei Wang, Feimin Ma, and Chun Li
DOI: 10.1002/spp2.1293
Addition Information

How to Cite

WANG, W., MA, F., LI, C. 2020. . Papers in Palaeontology, 6, 2, 251-264. DOI: /doi/10.1002/spp2.1293

Author Information

  • Wei Wang - Key Laboratory of Vertebrate Evolution & Human Origins CAS Center for Excellence in Life & Paleoenvironment Institute of Vertebrate Paleontology & Paleoanthropology Chinese Academy of Sciences Beijing 100044 China
  • Wei Wang - State Key Laboratory of Lithospheric Evolution Institute of Geology & Geophysics Chinese Academy of Sciences Beijing China
  • Feimin Ma - Erenhot Museum Nei Mongol 011199 China
  • Chun Li - Key Laboratory of Vertebrate Evolution & Human Origins CAS Center for Excellence in Life & Paleoenvironment Institute of Vertebrate Paleontology & Paleoanthropology Chinese Academy of Sciences Beijing 100044 China

Publication History

  • Issue published online: 25 April 2020
  • Manuscript Accepted: 13 October 2019
  • Manuscript Received: 11 April 2019

Funded By

Chinese Academy of Sciences. Grant Number: XDB26000000
National Natural Science Foundation of China. Grant Number: 41772006

Online Version Hosted By

Wiley Online Library
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Abstract

Placodonts are a group of turtle‐like animals, including placochelyids that are restricted entirely to the Triassic Tethyan realm. Their fossil remains are rare compared with other contemporaneous marine reptiles. Here, we report the first subadult specimen of the placochelyid Psephochelys polyosteoderma from south‐western China. It is the most complete specimen of this taxon known. The new fossil is referred confidently to Psephochelys polyosteoderma on the basis of the narrow and spatulate rostrum, toothless premaxillae, and carapace composed of small and numerous armour plates with relatively smooth surfaces. The new specimen provides additional anatomical information for Psephochelys polyosteoderma including the presence of transverse processes on the dorsal vertebrae lacking anteroposterior expansion, and a phalangeal formula in the pes of 1‐2‐3‐4‐2. The phylogeny of placodonts, especially the family Placochelyidae, is revised based on a character matrix incorporating additional postcranial characters. This resulted in a better‐resolved tree when compared with previous studies, with Psephochelys as a derived genus within Placochelyidae. On comparison with the adult holotype specimen, the incompletely developed armour in the new specimen reveals a fusion pattern of the carapace beginning with the axial and marginal regions. This surface fusion pattern resembles the ontogenetic process in the embryonic turtle shell, hinting at a possible deep homology with their common diapsid ancestor.

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