The Mio-Pliocene Pinniped Imagotaria

The new genus and species Imagotaria downsi is described from Mio-Pliocene rocks in coastal southern California and a new subfamily proposed to receive it, the Imagotariinae. The new species was too specialized to have given rise to any living pinniped. It had large lingual, cingular cusps on the postcanine teeth and a vagina processus styloidei, for reception of the hyoid arch into the confines of the auditory bulla, enlarged to a degree not found in living sea lions. Related more closely to walruses and early otariids than to living sea lions, I. downsi evidently represents an evolutionary line independently attaining the structural grade of sea lions through parallel evolution from an early common ancestor.The middle ear region is described in detail and some anatomical terms are defined in order to more fully emphasize basicranial structures. A referred specimen from the same geologic unit, the Sisquoc Formation, is mentioned and the distribution of I. downsi and related species in time and space is discussed.Comparisons of the skull, dentition, and especially the middle ear region are presented and a discussion of the present state of knowledge of otariid phytogeny emphasizes that many different kinds of otariids have existed in the past. Not all of these can easily be called walruses or sea lions. The wide adaptive spectrum now known within Otariidae is comparable to that within Phocidae.Diagnoses of subfamilies are given based upon basicranial features, and a provisional classification is offered. The Otariidae is revised to include: the old family Odobenidae as a subfamily; the subfamilies Desmatophocinae, Allodesminae, Dusignathinae, Imagotariinae, and Otariinae (including the old subfamily Arctocephalinae as a tribe). These subfamilies are diagnosed on the basis of many basicranial features newly found to be of importance in otariid systematics.A survey of putative North Pacific extinct Otariini suggests: Pontolis magnus is too specialized to be considered as an ancestor of Eumetopias; the "cf. Pontolis magnus" of Lyon (1941) is possibly a species of Pontolis; Eumetopias sinanoensis Nagao (1941) is a junior synonym of Allodesmus kernensis Kellogg (1922); a new genus Oriensarctos is proposed to receive the species Eumetopias watasei Matsumoto (1925); the "Allodesmus sp" of Kaseno (1951) is Eumetopias sp; and Eumetopias (?) kishidai Shikama (1953) is relegated to synonymy under Zalophus californianus (Lesson, 1828).Imagotaria downsi is related to Pontolis, and possibly more closely to Phocarctos hookeri and other southern hemisphere Otariini than to living northern Pacific species of Otariini. It is a relative of Desmatophoca oregonensis, descended from that or a related species and paralleling living sea lions.