<紀要論文>
Functional Evoltion of Otoscaphites puerculus (JIMBO) and Scaphites planus (YABE), Upper Cretaceous Ammonites

作成者
本文言語
出版者
発行日
収録物名
開始ページ
終了ページ
出版タイプ
アクセス権
Crossref DOI
概要 Otoscaphites puerculus (JIMBO) and Scaphites planus (YABE) occur abundantly in the Turonian of Hokkaido and south Sakhalin. The two species are nearly satisfied with an indispensable condition of the ...fossil population concept by reason of the characteristic in the mode of occurrence. Biometric and hydrostatic examinations on 42 samples for the two species from Naibuchi, Saku, Obira and Oyubari areas, have been made to obtain the quantitative data on their functional evolution. The analyses of individual relative growth of radius length to total rotation angle, septal and ventral wall thickness to radius length and variation of phragmocone size of adult shells indicate that the two species evolved in parallel in the direction of a buoyancy excess. Approximate calculation of the buoyancy of several well-preserved adult shells suggests that the two species changed with time in the mode of life of adult stage from benthic to planktic. The suture complexity of the two species increases with time in inverse proportion to the growth of septal and ventral wall thickness. Their inhabitable depth range may be shallower than that of modern Nautilus, because of their smaller value of the relative siphuncular strength than in Nautilus. Judging from the coexistent and sympatric mode of occurrences, similarity of ontogeny until 8 or 9π stage and parallel historical change of certain shell characters, it may be possible that the relationship between the two nominal species is a sexual dimorphism.続きを見る

本文ファイル

23_03_p367 pdf 3.72 MB 159  

詳細

PISSN
NCID
レコードID
査読有無
登録日 2015.11.11
更新日 2021.02.18

この資料を見た人はこんな資料も見ています