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The Pseudonautilidae is a family of Jurassic and Lower Cretaceous cephalopods belonging to the same major group as modern ''Nautilus'', the Nautilaceae, but forming a different branch from the Nautilidae. They were contemporary with ammonites (order Ammonitida) which comprise an entirely different set of shelled cephalopod stocks. Pseudonautilids are characterized by an involute, generally compressed, nautiliconic shell; highly sinuous "goniatitic" sutures; and siphuncle generally located between the center and venter. Three genera are included. * '' Pseudonautilus'': Shell involute, compressed; whorl section higher than wide, flanks flattened; venter broadly arched; umbilicus small and deep; suture with deep narrow ventral lobe, large V-shaped lateral lobes on either side followed by rounded saddles then smaller lobes just above the umbilical seam; siphuncle subventral. Found in Europe and North Africa. An almost perfect homeomorph of the Permian ''Permoceras''. Range as for family. * '' Pseudaganides'' Nautiliconic; whorl section subrectangular to compressed with flattened flanks converging toward a flattened to rounded venter; suture with ventral lobe and broad deep lateral lobes; siphuncle central to subcentral.. Found in the Jurassic of Europe and Pakistan. * ''Xenocheilus'' Like ''Pseudonautilus'' but with subangular ventral shoulders and rounded, rather than pointed, lateral lobes. From the Upper Jurassic and Lower Cretaceous of Europe and north Aftrica. ==References== * Bernhard Kümmel, 1964. Nauiloidea -Nautilida. Treatise on Invertebrate Paleontology Part K. Geological Society of America and University of Kansas Press, Teichert and Moore, (eds). * ( Pseudonautilidae -Paleodb ) Dec 2010 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pseudonautilidae」の詳細全文を読む スポンサード リンク
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