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The Polymorphitidae comprises a family of Early Jurassic ammonoid cephalopods that contribute to the Eoderocerataceae. Two subfamilies, the Polymorphtinae and Tropidoceratinae, are included. Polymorphitid ammonites produced typically evolute shells, which are more compressed than in most members of the superfamily. Many possess ventral chevrons and/or a fastigate venter resembling a gable roof, which in some develops into a true keel on the outer whorls. The Polymorphtinae is the larger and more diverse subfamily of the two. their shells have venters (outer rims) that may be smooth or ribbed, or have a median row of beading or serrations. The Tropidoceratinae, referred to as the Acanthopleuroceratinae in the Treatise L 1957, instead have a venter with a keel. ==References== * W. Arkell ''et al'', 1957. Mesozoic Ammonoidea, ''Treatise on Invertebrate Paleontology, Part L''. Geological Society of America and University of Kansas Press. * (family Polymorphitidae ) 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「Polymorphitidae」の詳細全文を読む スポンサード リンク
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