Dozens of mammalian finds have made the Messel Pit Fossil Site world famous. Forty-five species are already known and at least 60 species are expected to be described from the Messel Formation laid down during the period when the mammals were developing rapidly, after the extinction of the giant reptiles at the end of the Cretaceous. The number of mammal fossils is large compared with those at other European fossil sites of a similar geological age.