The origin and early evolution of turtles have long been major contentious issues in vertebrate zoology1,2,3,4,5,6,7,8,9,10,11. This is due to conflicting character evidence from molecules and morphology and a lack of transitional fossils from the critical time interval. The ∼220-million-year-old stem-turtle Odontochelys from China12 has a partly formed shell and many turtle-like features in its postcranial skeleton. Unlike the 214-million-year-old Proganochelys from Germany and Thailand, it retains marginal teeth and lacks a carapace. Odontochelys is separated by a large temporal gap from the ∼260-million-year-old Eunotosaurus from South Africa, which has been hypothesized as the earliest stem-turtle4,5. Here we report a new reptile, Pappochelys, that is structurally and chronologically intermediate between Eunotosaurus and Odontochelys and dates from the Middle Triassic period (∼240 million years ago). The three taxa share anteroposteriorly broad trunk ribs that are T-shaped in cross-section and bear sculpturing, elongate dorsal vertebrae, and modified limb girdles. Pappochelys closely resembles Odontochelys in various features of the limb girdles. Unlike Odontochelys, it has a cuirass of robust paired gastralia in place of a plastron. Pappochelys provides new evidence that the plastron partly formed through serial fusion of gastralia3,13. Its skull has small upper and ventrally open lower temporal fenestrae, supporting the hypothesis of diapsid affinities of turtles2,7,8,9,10,14,15.
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We acknowledge the Schumann family for their continued support and granting access to the Vellberg quarry, and F. Ullmann, B. Rozynek, W. Kugler, T. Haubold, U. Günter, and M. Salomon for assistance in the field and for donating specimens to the Staatliches Museum für Naturkunde Stuttgart. N. Klein and T. Scheyer assisted with the histological interpretation of the thin-sections. T. Lyson provided the character-taxon matrix used in ref. 5. I. Rosin, N. Adorf, M. Kamenz, and K. Krämer prepared the material, and C. Wimmer-Pfeil prepared thin-sections. We thank D. Seegis, H. Hagdorn, W. Joyce, N. Klein, T. Lyson, J. Müller, O. Rieppel, and T. Scheyer for discussions.
The authors declare no competing financial interests.
P. rosinae is in the ZooBank database (http://zoobank.org/) with Life Science Identifier urn:lsid:zoobank.org:act:CDD54976-047F-43AA-80F4-9680DF78CD7B.
Extended data figures and tables
a, b, Photograph and explanatory outline drawing of partial skull and postcranial skeleton of P. rosinae (SMNS 91356); c, left parietal in ventral view; d, right parietal in dorsal view; e, left postorbital; f, left postfrontal; g, left frontal. Abbreviations: dv, dorsal vertebra; f, frontal; ga, gastralium; j, jugal; mt, metatarsal; n, nasal; p, parietal; ph, phalanx; po, postorbital; pof, postfrontal; ti, tibia; tv, tail vertebra.
a, b, Photograph (a) and explanatory outline drawing (b) of associated skeletal remains of a very small individual of P. rosinae (SMNS 92066). Bones of the skull are shown in a darker shade of grey. Abbreviations: d, dentary; dv, dorsal vertebra; fe, femur; gas, gastralia; j, jugal; prf, prefrontal; pt?, possible pterygoid; ti, tibia.
a, b, Photograph (a) and explanatory outline (b) of a set of gastralia elements and fragments of two trunk ribs (black) that are part of the incomplete, partly articulated postcranial skeleton SMNS 91360.
Extended Data Figure 5 Tree illustrating hypothesis of turtle relationships based on the Tree Analysis using New Technology (TNT) program.
Individual nodes are numbered. For additional information refer to ‘Phylogenetic analysis’ section in Supplementary Information.
Extended Data Figure 6 Tree illustrating hypothesis of turtle relationships based on Bayesian analysis.
Numbers at individual nodes represent posterior probabilities. For additional information refer to ‘Phylogenetic analysis’ section in Supplementary Information.
This file contains additional specimen and locality data, a list of characters and character-states, information on phylogenetic analysis and additional morphological detail on trunk ribs. (PDF 599 kb)
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Schoch, R., Sues, HD. A Middle Triassic stem-turtle and the evolution of the turtle body plan. Nature 523, 584–587 (2015). https://doi.org/10.1038/nature14472
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