Postcrania of fossil carnivorans from the early Eocene of North America are described and compared to a locomotor-diverse group of small and medium-sized modern carnivorans using iwo approaches:​ traditional comparative anatomy and a cross-sectional analysis of the humerus and femur. The postcranial morphology of miacid and viverravid miacoids differ substantially and significant differences in both locomotor behaviors and substrate use are inferred.

Miacids are characterized by powerful limbs with well defined muscle insertion sites, and joints capable of a large range of motion. The latter is particularly marked at the glenohumeral, proximal radioulnar, hip, and ankle joints, where an increased range of motion is particularly important among those extant carnivorans that habitually use arboreal habitats. While most miacids, e. g. Miacis, Dodectes, Uintacyon, and Vassacyon, were probably equally adept in both terrestrial and arboreal habitats, middle Eocene members of Vulpavus are argued to have been more strictly arboreal similar and in this respect similar to the extant kinkajou (Potos) and binturong (Arctictis).

By contrast, the viverravid Didymictis was a habitually terrestrial and probably incipiently cursorial animal that likely utilized digging as well as quickness to catch prey. Joints of the fore- and hindlimb are modified for stability at the expense of mobility, but the limbs are not elongate indicating an animal that was probably similar in many ways to a large herpestid such as Ichneumia, the oriental civet Viverra, or the bush dog Speothos. Viverravus, postcrania for which were previously undescribed, shares morphologic characters with both Didymictis and miacids. Greater joint mobility at the hip and ankle indicate that this viverravid may have climbed more frequently than did Didymictis, but Viverravus was clearly more terrestrially adapted than any of the miacids.

Body mass estimates based on cross-sectional and diaphyseal diameters suggest that most of the early and middle Eocene carnivorans weighed between 1 and 10 kg. Among miacids Miacis and Oodectes were at the small end of the scale having body masses of between 1 and 3 kg, Vulpavus was larger weighing between a 3 and 8 kg and Vassacyon, the largest of the miacids, probably weighed about 10 kg. Didymictis, the only viverravid for which body mass estimates could be made, probably ranged in size from 4 to 8 kg.