Changes in Cretaceous ammonoid diversity and marine environments of the Japanese Islands

This study surveys 902 species of Cretaceous ammonoids in Japan, and identifies species diversity changes during 29 Japanese Cretaceous substages. The species diversity, fluctuates between the peak of 92 species in upper Albian and the lowest of less than 40 species in lower and middle Albian, upper Cenomanian, lower Coniacian and upper Campanian onward. More than half of these periods of the lowest diversity except that in the lowest and uppermost Cretaceous, correlate with oceanic anoxic events/subevents indicating that species diversity of the Japanese Cretaceous ammonoids was primarily controlled by such oceanic anoxic events/subevents.