2021年5月26日
The late Pliensbachian (Early Jurassic) ammonoid Amaltheus in Japan: systematics and biostratigraphic and paleobiogeographic significance
Journal of Paleontology
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- 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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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
- ID情報
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- DOI : 10.1017/jpa.2021.39
- ISSN : 0022-3360
- eISSN : 1937-2337