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Plectronoceras : ウィキペディア英語版 | Plectronoceras
}} ''Plectronoceras'' is the earliest known shelly cephalopod, dating to the Upper Cambrian. None of the fossils are complete, and none show the tip or opening of the shell.〔 Approximately half of its shell was filled with septa; 7 were recorded in a 2 cm shell. Its shell contains transverse septa separated by about half a millimetre, with a siphuncle on its concave side.〔 Its morphology matches closely to that hypothesised for the last common ancestor of all cephalopods.〔 ''Plectronoceras'' is the type genus of the family Plectronoceratidae. ==References==
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「Plectronoceras」の詳細全文を読む
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