Psiloceratoidea
Psiloceratoidea is a superfamily of Early Jurassic Ammonoidea, ammonoid cephalopods proposed by Alpheus Hyatt, Hyatt in 1867, assigned to the order Ammonitida. They were very successful during Hettangian and Sinemurian. Last of them, family Cymbitidae and genera ''Hypoxynoticeras'' and ''Radstockiceras'' survived into Pliensbachian, Early Pliensbachian. Psiloceratoidea is probably derived from the family Ussuritidae, which were Triassic members of Phylloceratoidea. Similar to their ancestors, Psiloceratidae kept smooth, rounded venter for whole of their life. Schlotheimiidae were different, as they had ventral chevrons. Rest of the families had angular venter, or keel for at least part of their ontogeny. Most of the members of this superfamily had only simple ribs, but few of them have evolved also secondary ribbing. While some members are involute and some Oxynoticeratidae were oxycone, most of the species were evolute. Families *Psiloceratidae - Evolute shells with simple, o ...
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