Protoglobicephala mexicana, a new genus and species of Pliocene fossil dolphin (Cetacea; Odontoceti; Delphinidae) from the Gulf of California, Mexico

摘要

The Delphinidae is the most diverse living family of odontocete cetaceans and includes modern oceanic dolphins and their fossil relatives. In contrast, the world-wide fossil record of this family is sparse when compared to that of several other cetacean groups, and relatively few extinct delphinids have been formally named. Most of the known fossil Delphinidae are of Pliocene age, and most of these are from Europe. We describe a new genus and new species of extinct Delphinidae, Protoglobicephala mexicana, based on a cranium of Pliocene age, between approximately 2 and 3 million years old, from Isla San Jose in the Gulf of California, Baja California Sur, Mexico. This species shares with Recent species of Globicephala wide exposures of the premaxillae on the dorsal surface of the rostrum and rugose areas on the distal ends of the premaxillae. Like other Globicephalinae members, it is a relatively large animal and has a wide cranium, short and broad rostrum, and relatively few teeth that are of relatively large size. It also shares some similarities with the generalized delphinine delphinid Tursiops. These similarities and the geochronologically relatively young occurrence of this new species reinforce previous notions that the present taxonomic diversity of the family Delphinidae is the result of rapid evolutionary diversification since Miocene time, or within approximately the past five million years. The ability of living species of Delphinidae in different genera, and in different nominal subfamilies, to mate and to produce viable hybrid offspring, offers additional support for the idea of rapid and recent evolutionary diversification of this family.