Pachyaena

showing the position of the Mesonychia The genus' greatest diversity is seen in North America, with P. ossifraga known from Latest Paleocene strata of Wyoming, and P. gigantea, P. intermedia, and P. gracilis known from Early Eocene strata of Wyoming. P. nemegetica is known from Late Paleocene strata of Mongolia. However, a 2007 paper suggests that Pachyaena may be paraphyletic, with P. ossifraga being closer to Synoplotherium, Harpagolestes and Mesonyx than to P. gigantea. Mesonychians recovered by Spaulding et al. (2009),which recovers the order outside of ungulates.}} }}|barend1=blue }} }} }} }} }} }} }} }} }}}}}} == Description ==

Size Pachyaena was one of the largest known mammals from the Early Eocene. P. gracilis was roughly the size of a wolf, with a mean body mass of , making it smaller than a few Wasatchian mammals. The larger species within the genus were about the size of moderately sized bears. However, O'Leary and Rose found even larger sizes for P. ossifraga. With the average body mass of , although individuals could’ve also reached . Postcranial anatomy The scapula of Pachyaena has been recovered, however even the most complete scapula was fragmented and incomplete. The glenoid fossa was symmetrically pyriform within the genus. Within the larger species, it was three-fourths as wide as it is long. In P. gracilis, it was found to have been somewhat narrow compared to the larger species. Compared to Canis, the suprascapular notch was relatively shallow. The humerus exhibited many characteristics of cursoriality. Despite being relatively robust, the humeral shaft and articular surfaces are modified to reduce most muscular prominences, which limited movement to the sagittal plane. The greater tuberosity is prominent and projects above of the head, although less so in P. gracilis than in larger species, which is a characteristic seen in ungulates and non-ungulate cursorial carnivorous mammals. == Paleobiology ==

Locomotion Analysis of three wolf to bear-sized species from the early Eocene of Wyoming (Willwood Formation) indicates they all had many adaptations for running, including paraxonic compressed feet with a vestigial first digit, lower sections of the limbs elongated compared with the upper sections, and limb joints with movement mostly restricted to a sagittal plane (back-and-forth movement). All these characteristics are common to both ungulates that run to escape predators and carnivores that run to pursue prey, though they probably evolved independently in mesonychids. Some adaptations are more typical of the grade of cursorial carnivores; others are more specialized, as in ungulates. Pachyaena was likely built for endurance rather than speed; the overall body shape of the genus would have resembled a modern tapir. Despite this, Pachyaena probably wasn’t a derived carnivore due to the lack of carnassials for eating fresh meat and it’s not particularly fast dilocomotory locomotion. ==References==