4-583: The Xenodiscidae are the earliest of the Ceratitida and comprise Middle and Upper Permian genera characterized by compressed, discoidal, evolute shells with rounded to acute venters and commonly with lateral ribs. Sutures are goniatitic to weakly ceratitic. The Xenodiscidae, which are part of the superfamily Xenodiscoidea , are derived from the Daraelitidae , a family in the Prolecanitida (ibid). In turn,
8-530: A few the sutures are goniatitic while in others they are ammonitic. Only eight superfamilies are shown in the Treatise on Invertebrate Paleontology , Part L,(1957), the Otocerataceae, Noritaceae, Ceratitaceae, Arcestaceae, Clydonitaceae, Lobitaceae, Ptychitaceae, and Tropitaceae, in text sequence. The other 10 have been added since, derived from within the original eight. This Ceratitida -related article
12-674: The Xenodiscidae provided the root stock for the subsequent expansion and diversification of the Ceratitida in the Triassic. This Ceratitida -related article is a stub . You can help Misplaced Pages by expanding it . Ceratitida See text Ceratitida is an order that contains almost all ammonoid cephalopod genera from the Triassic as well as ancestral forms from the Upper Permian ,
16-451: 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 uncoiled. Sutures are typically ceratitic, with smooth saddles and serrate or digitized lobes. In
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