PARTIAL SKELETON OF THE PRIMITIVE CARNIVORAN MIACIS-PETILUS FROM THE EARLY EOCENE OF WYOMING

A partial skeleton of Miacis petilus, a primitive carnivoran from the early Eocene (Wasatchian) Willwood Formation of the Bighorn Basin, Wyo ming, is described. This is the oldest skeleton reported for Miacis, a genus that lies at or near the base of the family Miacidae, from whic h all caniform Carnivora (and possibly all living Carnivora) are deriv ed. Anatomical comparisons to modern carnivorans suggest that M. petil us was as well adapted for exploiting arboreal habitats as almost any extant member of the order. A weight estimate of 1.3 kg is calculated for this individual based on regressions of body mass against humeral and femoral cross-sectional properties derived for small-bodied arbore al and scansorial carnivorans. Differences in estimates of body mass f or two individuals of the middle Eocene Miacis parvivorus imply that t his species was dimorphic in size.