6-657: Phylloceratidae is the predominant family of the Phylloceratina with some 15 or more genera found in rocks ranging from the Lower Jurassic to the Upper Cretaceous . Members of the Phylloceratidae are characterized by smooth, involute shells with very thin walls. Many are covered with fine growth lines but are usually without ribbing. Sutures are complex with the major and minor branches of
12-735: The Ammonitida , whose range extends from the Lower Triassic to the Upper Cretaceous . Shells of the Phylloceratina are generally smooth with small to large umbilici and complex sutures with leaf-like phylloid saddle endings and lobes with thorn-like projections. The Phylloceratina are most likely derived from the Ceratitid Deineroceratidae, which is thought to have given rise early in the Triassic to
18-451: The Phylloceratidae vary in complexity and are usually described on the basis of the saddles, which diverge to the front. Saddle endings may be double (diphyllic), triple (triphyllic), or quadruple (tetraphillic). Branching may be asymmetric. Intervening lobes are variably branched with thorn-like or spinose terminations as viewed in plan. Phylloceratina The Phylloceratina comprise a suborder of ammonoid cephalopods, belonging to
24-683: The Ussuritidae. The Ussuritidae is the ancestral family of the Phylloceratina. The Ussuritidae extend through the Upper Triassic but not into the Jurassic, and gave rise to the Upper Triassic Discophyllitidae. The Discophyllitidae is the probable source for the L Jurassic - U Cretaceous Phylloceratidae and possibly for the L Jurassic Juraphyllitidae. The Phylloceratina gave rise early in the Jurassic through
30-712: The early Lower Jurassic Peluroacanthitidae and Ectocentridae. The Phyloceratidae also gave rise at or near the beginning of the Jurassic to the Psiloceratoidea which unites families of the Early Jurassic Ammonitina . Other Jurassic Ammonitina are derived from the Lytoceratina. Later, phylloceratids are said to have given rise to Cretaceous Ammonitina included in the Desmoceratoidea , Hoplitoidea , and Acanthoceratoidea . Sutures in
36-619: The saddles with phylloid or spatulate endings. The Phylloceratidae are probably derived from the Late Triassic Discophyllitidae by increasing the sutural complexity and evolving involute coiling. The Discophyllitidae in turn have their origin in the Ussuritidae , also known as the Monophyllitidae. The Phylloceratidae gave rise at or near the beginning of the Jurassic to the ancestral Lytoceratina ,
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