Revision of Yabeiceras, a Coniacian (Late Cretaceous) ammonite genus, based on material from the type locality in Fukushima, Japan

The uncommon Coniacian ammonite genus Yabeiceras is re-examined systematically on the basis of 11 specimens, including the neotype, from the type locality of the genus (Sakurazawa Valley, Hirono), as well as from a fossil locality of the Ammonite Centre at Iwaki (Fukushima Prefecture, Japan). Three species are identified: Y. orientale Tokunaga and Shimizu, 1926, Y. kotoi Tokunaga and Shimizu, 1926 and Y. cf. manasoaense Collignon, 1965. In addition to presenting systematic descriptions of these species, we discuss ontogenetic changes in ornament and the morphological range of variation of Y. orientale, as well as the possibility of sexual dimorphism within the genus.