Full text loading...
Paleontological Research
Abstract
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.
We thank Ken-ichi Chiyokawa for donating the specimen to the Hobetsu Museum. We are grateful to the museum for permission to use their specimen for destructive analysis, and former and current curators Tsutomu Chitoku and Kazuhiko Sakurai for assisting various aspects of our research. Two anonymous reviewers provided constructive comments and suggestions which improved our manuscript considerably. Chisako Sakata and Makoto Manabe (National Museum of Nature and Science) are thanked for assistance in the use of the CT-scanner, and Koichiro Fujimoto, Masataka Nakata (Tokyo Gakugei University) and Takanobu Tsuihiji (University of Tokyo) for assistance in the use of laboratory equipment. We also thank Yasuhisa Nakajima and Momo Yamashita (University of Tokyo) for their helpful advice, and Janet and David Gillette of the Museum of Northern Arizona for access to comparative specimens. Financial support was provided by the Inaniori Foundation and Tokyo Gakugei University (to TS), JSPS KAKENHI grants 15K05327 (to TS) and 26800270 (to SH).
Data & Media loading...