ANATOMY OF THE POSTCRANIAL SKELETON OF MIACIS UINTENSIS (MAMMALIA: CARNIVORAMORPHA)

This paper provides the first detailed description of the only known postcranial skeletal elements of Miacis uintensis. The morphology of the skeleton differs markedly from previously described miacids (a paraphyletic assemblage of early fossil carnivoramorphans), invalidating the notion that all miacids were very similar in their postcranial morphology and locomotor styles. The majority of the differences indicate an animal less well adapted to an arboreal lifestyle than has been inferred for other early miacid carnivoramorphans. A phylogenetic analysis clearly nests Miacis uintensis within the paraphyletic array of taxa previously referred to as the Miacidae, in a position closer to the crown clade Carnivora than is Vulpavus, a miacid whose postcranium has been previously described. When compared with the early canid Hesperocyon, this specimen shares many features thought to relate to the acquisition of a more terrestrial mode of life. This result indicates that, in contrast to prior models suggesting arboreality for all miacids, at least one independent 'descent from the trees' occurred much earlier within the array of stem carnivoramorphan taxa.