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1 July 2018 A Turonian Polycotylid Plesiosaur (Reptilia: Sauropterygia) from Obira Town, Hokkaido, and Its Biostratigraphic and Paleoecological Significance
Tamaki Sato, Tomoya Hanai, Shoji Hayashi, Tomohiro Nishimura
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Abstract

The Polycotylidae are short-necked plesiosaurs known from the Cretaceous in various parts of the world, but only a few occurrences have been documented in Japan, where elasmosaurid remains are much more common. An indeterminate polycotylid specimen from the Upper Cretaceous in Obira Town, Hokkaido, is described. Characteristics of the vertebrae and clavicular arch support its taxonomic affinity. The Turonian occurrence of the specimen indicates the continuous presence of the Polycotylidae across the Cenomanian-Turonian boundary in the northwestern Pacific. Macroscopic osteological features of the vertebrae and clavicular arch indicate an advanced stage of ossification, and there are histological characteristics suggesting slowed growth. The osteoporotic-like condition implies a high degree of aquatic adaption.

© by the Palaeontological Society of Japan
Tamaki Sato, Tomoya Hanai, Shoji Hayashi, and Tomohiro Nishimura "A Turonian Polycotylid Plesiosaur (Reptilia: Sauropterygia) from Obira Town, Hokkaido, and Its Biostratigraphic and Paleoecological Significance," Paleontological Research 22(3), 265-278, (1 July 2018). https://doi.org/10.2517/2017PR024
Received: 13 December 2016; Accepted: 20 November 2017; Published: 1 July 2018
JOURNAL ARTICLE
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KEYWORDS
Cenomanian-Turonian boundary
Histology
ontogeny
Plesiosauria
Polycotylidae
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