A revision of Tapocyon (Carnivoramorpha), including analysis of the first cranial specimens and identification of a new species

Abstract

Three new specimens of Tapocyon are described from Middle Eocene (Uintan NALMA) strata of San Diego County, California. These specimens include the first cranial material for the genus, significantly increase the knowledge of the anatomy of Tapocyon and enhance understanding of the phylogeny of this taxon and other early carnivorans. Tapocyon can be placed tentatively within the Caniformia (Carnivora, Mammalia) based on the following combination of characters: reduced parastyle and protocone on P4; continuous lingual cingulum on upper molars; retention of M3/3; short m2 talonid; moderately deep and narrow metastyle notch on P4; and hypoconid larger than hypoconulid on m2. The revision presents new diagnoses of Tapocyon and included species, synonymizes T. occidentalis with T. robustus, and erects a new species, T. dawsonae. The revision expands the geographic range of T. robustus during a time of hypothesized increasing provinciality. Although no auditory bullae are preserved, the basicranium of one of the new specimens shows evidence of a likely ossified, but loosely attached ectotympanic and entotympanic bulla, expanded primarily in the posterior direction. The majority of the postcranial skeleton is preserved in one new specimen, for which we provide preliminary observations of the morphology of the middle and distal phalanges, which indicate that Tapocyon had retractable claws.