A new Miocene pinniped in the genus Prototaria (Carnivora: Odobenidae) from the Moniwa Formation, Miyagi, Japan

ABSTRACT

A new fossil odobenid skull from the late early or early middle Miocene age Moniwa Formation, Miyagi Prefecture, northern Japan, represents a new species of the genus Prototaria Takeyama and Ozawa, 1984. Prototaria planicephala, sp. nov., is distinguished from P. primigena Takeyama and Ozawa, 1984, by having a dorsoventrally flattened cranium with a wider rostrum, more derived cheek teeth, and a flattened tympanic bulla. These and other differences indicate that P. planicephala is a more derived species than P. primigena. The species of Prototaria lack many of the derived characters seen in the genus Neotherium Kellogg, 1931, which is interpreted as a closely related genus.

Cladistic analysis of 25 cranial and dental characters suggests that the family Odobenidae form a monophyletic clade, united by a dorsoventrally thick and posterolaterally expanded pterygoid strut, a bony tentorium closely appressed to the petrosal, and molarized premolars with lingually expanded cingula resulting in near cheek tooth homodonty. Although the Dusignathinae and the Odobeninae are separate monophyletic subfamilies, the “Imagotariinae” are not monophyletic, and are regarded as a paraphyletic basal group.

The genus Prototaria is a basal taxon within the family Odobenidae, which had an earlier evolutionary history in the middle Miocene in the western North Pacific than in the eastern North Pacific.