論文

査読有り
2021年5月26日

The late Pliensbachian (Early Jurassic) ammonoid Amaltheus in Japan: systematics and biostratigraphic and paleobiogeographic significance

Journal of Paleontology
  • Kentaro Nakada
  • ,
  • Michiharu Goto
  • ,
  • Christian Meister
  • ,
  • Atsushi Matsuoka

開始ページ
1
終了ページ
18
記述言語
掲載種別
研究論文(学術雑誌)
DOI
10.1017/jpa.2021.39
出版者・発行元
Cambridge University Press (CUP)

<title>Abstract</title>
The genus <italic>Amaltheus</italic>, one of the representative late Pliensbachian ammonoids, has biostratigraphic and paleobiogeographic significance in Japan. Four species, <italic>Amaltheus stokesi</italic> (Sowerby, 1818), <italic>A. margaritatus</italic> de Montfort, 1808, <italic>A. repressus</italic> Dagis, 1976, and <italic>A. orientalis</italic> new species, have been found in the Kuruma Group in central Japan; <italic>A. stokesi</italic> and <italic>A. margaritatus</italic> are also from the Toyora Group in southwest Japan. On the basis of taxonomic analysis of the genus <italic>Amaltheus</italic>, we distinguish two successive ammonoid biozones in the lower part of the Teradani Formation of the Kuruma Group: the <italic>Amaltheus stokesi</italic>–<italic>Amaltheus repressus</italic> and the <italic>Amaltheus margaritatus</italic> assemblage zones, in stratigraphic ascending order. This study also establishes the presence of the <italic>Amaltheus stokesi</italic> Assemblage Zone in the Higashinagano Formation of the Toyora Group. The <italic>stokesi</italic>–<italic>repressus</italic> and the <italic>stokesi</italic> assemblage zones correspond biostratigraphically to the <italic>Amaltheus stokesi</italic> Standard Subzone of the <italic>margaritatus</italic> Zone. The <italic>margaritatus</italic> Assemblage Zone is correlated with the <italic>Amaltheus subnodosus</italic> and <italic>Amaltheus gibbosus</italic> standard subzones. The Japanese early–middle late Pliensbachian ammonoid faunas are composed almost entirely of pan-Boreal and Arctic species of the genus <italic>Amaltheus</italic>. This faunal composition has an affinity with that of the Northeast Russian region, and thus suggests a strong paleobiogeographic relationship between East Asian and Northeast Russian faunas throughout this time interval.


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リンク情報
DOI
https://doi.org/10.1017/jpa.2021.39
URL
https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022336021000391
ID情報
  • DOI : 10.1017/jpa.2021.39
  • ISSN : 0022-3360
  • eISSN : 1937-2337

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