The Genus Alatyroceras gen. nov. (Ammonoidea: Cardioceratidae, Arctocephalitinae) from the Upper Bathonian (Middle Jurassic) of the Russian Platform

A new genus Alatyroceras is established for the species A. nageli (Mitta) (type species of the genus), A. keuppi (Mitta), A. efimovi (Mitta), and A. infimum (Gulyaev et Kiselev), in Central Russia characterizing the interval correlated with the Upper Bathonian Variabile and Calyx zones of East Greenland. According to the refined data, the Keuppi Zone of the Russian Platform includes (from bottom to top) the efimovi, nageli, and keuppi faunal horizons. The genus Alatyroceras [M] completes the phylogenetic lineage Arcticoceras → Alatyroceras in the subfamily Arctocephalitinae; the name Costacadoceras Rawson is common to all microconchs of the subfamily.