Early Cenomanian (Cretaceous) ammonoids Utaturiceras and Graysonites from Hokkaido, North Japan (Studies of the Cretaceous ammonites from Hokkaido and Sakhalin-XCV).

Abstract

Three species of the ammonoid genus Utaturiceras, including U. chrysanthemum sp. nov.,and two species of Graysonites, from the Soeushinai area of northwestern Hokkaido, are described under revised diagnoses of the genera. They form the basal subzone of the Cenomanian sequence of strata in the studied area. This faunule is recognized in restricted parts of Japan and the correlatable faunule is also known in certain particular provinces of long distance in the world. The reason for this fact is discussed to some extent.