A revision of the Early Carnian Trachyceratidae (Ammonoidea) of Northeastern Asia

Major morphological features of the shell are studied, and new trachyceratid genera, Boreotrachyceras gen. nov. with the type species B. omkutchanicum (Bytschkov) and Okhototrachyceras gen. nov. with the type species O. seimkanense (Bytschkov), are established based on material from the Lower Carnian of the Omolon Massif and Northern Okhotsk Region. The first record of the genus Trachyceras in the Boreal Realm allows the correlation of the omkutchanicum Zone of Northeastern Asia with the standard aon Zone.