ニホンアシカZalophus californianus japonicusの頭骨の新資料について〔英文〕

概要

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New cranial materials of the Japanese sea lion, Zalophus californianus japonicus (PETERS, 1866), were studied, and cranial measurements, number of postcanine teeth and degree of suture closure in skull were examined in seven skulls and eight halves of mandible of the sea lion, excavated in 1950 at the Aonae Site in Okushiri Island, Hokkaido (Tables 1 and 2) . The present specimens were judged to be skulls of full-grown male Zalophus, and were identified as the species already known as the Japanese sea lion. It was found that the Japanese skulls are larger in size and wider in proportion to their length in a few measurements than the Californian ones, Z. c. californianus (LESSON, 1828) and the Galapagos ones, Z. c. wollebaeki SIVERTSEN, 1953, and also have a larger number in upper postcanine teeth than the former. Accordingly it seems neccessary to reexamine the classification of the Japanese sea lion in detail.