Principal ammonoid assemblages of Carboniferous period

Ammonoids constituted one of the most important marine faunal groups in the Carboniferous period; their assemblages can be used to identify and substantiate the main biostratigraphic boundaries of and within the Carboniferous system. The Devonian-Carboniferods boundary is marked by the extinction of ammonoids of the order Clymeniida and,other Devonian,types and the appearance of the suborder Prolecanitina. During the Early Carboniferbus epoch five major faunal assemblages were present, in ascending order: the Gattendorf (6 genera), Tournaisian (9 genera), Saourian (14 genera), Viséan (28 genera), and Namurian (47 genera). The boundary between the Early and Late Carboniferous is marked by general decrease in taxonomic variety and emergence of genera with more complex sutures (10 to 20 lobes). The major faunal assemblages during the Late Carboniferous epoch include the Bashkirian (28 genera), Moscovian (24 genera), Zhigulian (36 genera), and Orenburgian (27 genera). The upper boundary of die Carboniferous is not nearly so sharply expressed in terms of ammonoid changes as the lower one. AVailable eVidenCe 'favors' -placing it at the top of the Orenburgian stage, as the principal families of Permian ammonoids are all present in the overlying beds of the Asselian stage. Two new genera are diagnosed briefly; Winchelloceras n. gen. (type species, Goniatites allei Winchell, 1862) and Arcanoceras n. gen. (type species, Girtyoceras burmai Miller and Downs, 1950) and one new family, Orulganitidae (genus Orulganites). -- M. Gordon, Jr.