Abstract

Fossil crania from the late middle or early late Miocene (ca. 12–10 Ma) Ichibangawa Formation, Hokkaido, northern Japan, are described as a new genus and species of the archaic odobenid, Pseudotaria muramotoi, gen.et sp. nov. Pseudotaria muramotoi is characterized by having a dorsoventrally thick, posterolaterally expanded pterygoid strut, bony tentorium appressed to the petrosal (odobenid synapomorphies), double-rooted M1, reduced pseudosylvian fossa, and transversely arched palate (basal odobenid synapomorphies), and by retention of double-rooted premolars, except the P1. A phylogenetic analysis reveals that P. muramotoi possesses basal odobenid synapomorphies but lacks synapomorphies of the later diverging odobenids, and therefore, the taxon is nested in the paraphyletic stem group within the Odobenidae. The analysis also indicates that P. muramotoi might be viewed as a metataxon that shows the least modified condition in the transformation series to the later diverging odobenids.