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An early polycotylid plesiosaur (Reptilia: Sauropterygia) from the Cretaceous of Hokkaido, Japan

Published online by Cambridge University Press:  20 May 2016

Tamaki Sato
Department of Geology, University of Cincinnati, PO Box 210013, Cincinnati, Ohio 45221–0013
Glenn W. Storrs
Cincinnati Museum Center, Geier Collections and Research Center, 1720 Gilbert Avenue, Cincinnati, Ohio 45202, USA


A partial skeleton of a short-necked plesiosaur excavated from the Upper Cenomanian of the Middle Yezo Group of Hokkaido, Japan, includes disarticulated vertebrae, the right half of the pectoral girdle, fragments of the pelvic girdle, ribs, gastralia, and gastroliths. Gastroliths are unusual in short-necked plesiosaurs. Skeletal characters indicate that the specimen belongs to the Family Polycotylidae, well known from North America, the former Soviet Republics, and possibly from New Zealand. They are rare in East Asia and hitherto unknown from Japan. Extensive ossification indicates that this specimen is an adult individual, yet it is smaller than the adult specimens of other known polycotylids. The elongated epipodial bones are a unique character of the specimen but are probably plesiomorphic. The fossil is evidence of biogeographical diversification of the family at the beginning of the Late Cretaceous.

Research Article
Copyright © The Paleontological Society

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Present address: Department of Geology and Geophysics, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada, and Royal Tyrrell Museum of Paleontology, P.O. Box 7500, Drumheller, AB, T0J 0Y0, Canada.


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