樺太産Desmostylus mirabilisの骨格 : II. 腰椎・仙骨・尾椎

概要

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The lumbar vertebrae, sacrum and coccygeal vertebrae of Desmostylus mirabilis NAGAO from Keton are described with a discussion on its vertebral formula. The characteristics of the lumbar vertebrae are nearly the same as in the thoracics (INUZUKA, 1980) but the following differences are observed: Body is wider; costal processes short, depressed dorso-ventrally, protruded horizontally and at right angle ; spinous process longer foreand-aft, inclined forward slightly, not broadened transversely at the tip; accessory processes absent. Sacrum is composed of five segments, the first two of which form auricular surface; outline of sacrum triangular; a broad interarcuate space present between the first and the second segments; sacral ridge not so developed; spirous process not high. Coccygeal vertebrae is short; vertebral arch and transverse processes not developed; hemal arch probably absent. The vertebral formula of Desmostylus, 7-13-4-5-11, as confirmed by the present study, is very peculiar, being different from any of Sirenia, Proboscidea, Monotremata and Perissodactyla.
地学団体研究会の論文
1980-09-25