A review of Maastrichtian ammonite ranges

Although Maastrichtian ammonite diversity was lower than that of the Campanian Age, the purported long-term diversity reduction of ammonites near the end of the Cretaceous may be more a product of sea-level change than evidence of a long-term slide toward extinction in this group. Examination of four geographic regions with exposed Cretaceous/Tertiary boundaries shows the presence of at least 22 species of ammonites within several meters or less of the K/T boundary. The exact level of ammonite extinction, however, cannot yet be determined; in no section can ammonites be demonstrated to disappear synchronously with the rapid extinction of planktonic foraminiferans and coccoliths occurring at the end of the Cretaceous.