Xenoceltitidae, Kartoniert / Broschiert

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Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Xenoceltitidae are evolute, generally ribbed, upper Lower Triassic Ceratitida with ceratitic or goniatitic sutures; formerly included in the Noritaceae but now placed in the Xenodiscaceae. The Ceratitida is an order that contains almost all ammonoid cephalopod genera from the Triassic as well as ancestral forms from the Upper Permian, the exception being the phylloceratids which gave rise to the great diversity of post Triassic ammonites. Ceratitids overwhelmingly produced planospirally coiled discoidal shells that may be evolute with inner whorls exposed or involute with only the outer whorl showing. In a few later forms the shell became subglobular, in others, trochoidal or uncoilded. Sutures are typically ceratitic, with smooth saddles and serrate or digitized lobes. In a few the sutures are goniatitc while in others they are ammonitic.