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Kappachelys okurai gen. et sp. nov., a New Stem Soft-Shelled Turtle from the Early Cretaceous of Japan

Chapter
Part of the Vertebrate Paleobiology and Paleoanthropology book series (VERT)

Abstract

Kappachelys okurai gen. et sp. nov. is named and described based on two isolated carapacial elements (right seventh costal and left seventh peripheral) from the Lower Cretaceous (?upper Neocomian) Akaiwa Formation of west-central Honshu, Japan. Kappachelys is a small turtle (shell length ~10 cm) that exhibits a unique combination of three features: coarse and deep vermiculate sculpture on carpace; no scute sulci; and well-developed peripherals. The form of the sculpture and lack of scute sulci both suggest affinities with the Trionychidae (soft-shelled turtles), whereas the plesiomorphic retention of well-developed peripherals indicates Kappachelys lies outside the Trionychidae. Given this combination of primitive and derived features, we interpret Kappechelys as a stem trionychid. In the same region of Japan, the overlying Lower Cretaceous (Aptian) Kitadani Formation contains some of the oldest known, unequivocal trionychid fossils. Based on its slightly older age, similar geographical distribution, and more primitive shell morphology, Kappachelys could be ancestral to the trionychids of the Kitadani Formation.

Keywords

Early Cretaceous Japan Kappachelys Trionychidae  Trionychoidea 

Notes

Acknowledgments

We are especially grateful to Masatoshi Okura for the collection and preparation of turtle fossils, including the two specimens of Kappachelys. We also thank: T. Sonoda (Ibaraki University, Mito), M. Onodera (Kagoshima University, Kagoshima), and R. Obata (Wakasa-cho) for their help with excavations at the Oarashidani fossil locality; I. G. Danilov (Zoological Institute of the Russian Academy of Sciences, St. Petersburg) for access to comparative specimens; Y. Nakajima (Tokyo University, Tokyo) for sharing preliminary results from his histological studies on early trionychid shells; and I. G. Danilov, P. A. Meylan (Eckerd College), J. F. Parham (Alabama Museum of Natural History), and an anonymous reviewer for their comments and corrections on the submitted version of our manuscript. Field work at the Oarashidani fossil locality was supported by a Grant-in-Aid for Specially Promoted Research (awarded to M. Manabe of the National Science Museum, Tokyo: grant no. 12800018) from the Japanese Ministry of Education and Science.

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Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  1. 1.School of International Liberal StudiesWaseda UniversityTokyoJapan
  2. 2.Natural History Museum and InstituteChibaJapan
  3. 3.Shiramine Institute of PaleontologyIshikawaJapan

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