Partial Skeleton of the Primitive Carnivoran Miacis petilus from the Early Eocene of Wyoming

Abstract

A partial skeleton of Miacis petilus , a primitive carnivoran from the early Eocene (Was-atchian) Willwood Formation of the Bighorn Basin, Wyoming, is described. This is the oldest skeleton reported for Miacis , a genus that lies at or near the base of the family Miacidae, from which all caniform Carnivora (and possibly all living Carnivora) are derived. Anatomical comparisons to modern carnivorans suggest that M. petilus 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 arboreal and scan-sorial carnivorans. Differences in estimates of body mass for two individuals of the middle Eocene Miacis parvivorus imply that this species was dimorphic in size.