Mosirites, a New Cretaceous Heteromorph Ammonoid Genus from Hokkaido, Japan

A new genus Mosirites is herein erected for a Cretaceous heteromorph ammonoid that ranges from the upper Albian to the lower Cenomanian of Hokkaido. The new genus differs from previously described genera of the family Anisoceratidae by its large, loosely coiled, early helical whorls followed by loosely coiled elliptical planispiral whorls. Two new species, M. serpentiformis sp. nov. and M. mirabilis sp. nov., are described from the upper Albian and the upper Albian to lower Cenomanian interval, respectively. Mosirites was probably derived from Anisoceras during late Albian time and flourished during late Albian to early Cenomanian time in the North Pacific region.