Morphological and histological evidence for the oldest known softshell turtles from Japan

Yasuhisa Nakajima, Igor G. Danilov, Ren Hirayama, Teppei Sonoda, Torsten M. Scheyer

Research output: Contribution to journalArticle

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Abstract

Herein we report morphologically and histologically diagnostic trionychid specimens from the Barremian–Aptian (129.4–113.0 Ma) of Japan. One specimen (FPDM-V9487) is an associated skeleton that consists of a scapula, a humerus, an ischium, and hypoplastra. The limb and girdle bones are similar in morphology to those of modern trionychids. The hypoplastron also resembles that of modern trionychids; however, it is distinctive in that it completely lacks callosities. The other three new specimens are fragmentary costals that show a reduction in the shell bones and an absence of scute sulci. Two of the newly reported costals and FPDM-V0127 were examined histologically. Bone fiber bundles organized in a plywood-like structure, which is unique to trionychids, were identified. Fossil occurrence data indicate that morphologically and histologically typical trionychids already inhabited the coastal region of Asia (e.g., western Japan) as early as the Aptian. In contrast, the Hauterivian–Aptian stem trionychid Kappachelys okurai from Japan does not show a plywood-like shell microstructure, suggesting that K. okurai could be the earliest-branching taxon of known stem trionychids or a carettochelyid. Our paleobiogeographic compilation suggests that the spread of wetlands in the Northern Hemisphere and the high global temperature during the middle Cretaceous (Aptian–Turonian, 125.0–89.8 Ma) might have contributed to the dispersal of trionychids from Asia, allowing for the establishment of this modern freshwater reptilian fauna. Citation for this article: Nakajima, Y., I. G. Danilov, R. Hirayama, T. Sonoda, and T. M. Scheyer. 2017. Morphological and histological evidence for the oldest known softshell turtles from Japan. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1278606.

Original languageEnglish
JournalJournal of Vertebrate Paleontology
DOIs
Publication statusAccepted/In press - 2017 Apr 10

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turtle
bone
stem
shell
paleontology
Aptian
skeleton
limb
Northern Hemisphere
microstructure
vertebrate
wetland
fossil
fauna
Cretaceous
temperature

ASJC Scopus subject areas

  • Palaeontology

Cite this

Morphological and histological evidence for the oldest known softshell turtles from Japan. / Nakajima, Yasuhisa; Danilov, Igor G.; Hirayama, Ren; Sonoda, Teppei; Scheyer, Torsten M.

In: Journal of Vertebrate Paleontology, 10.04.2017.

Research output: Contribution to journalArticle

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