“Stout Hyena”
Species: Pachyaena gigantea, Pachyaena intermedia, Pachyaena ossifraga, Pachyaena gracillis
Time Period: Early Eocene (55 MYA)
It is believed Pachyaena originated in Asia and spread outwards to Europe and then North America when sea levels were low, exposing a land bridge across the Bering straits. Species of Pachyaena varied in size from smaller, wolf sized animals to large bear sized ones. Diet may have been as varied as size, with smaller species being strictly carnivorous and larger ones being omnivorous. All species, however, had strong jaws, which were used for tearing flesh or grasping prey, and some may have been both hunters and scavengers. There is however, no evidence of bone crushing strength in jaws, as is seen in other Mesonychids such as Andrewsarchus.
The body of Pachyaena was heavily built, which indicates hunting species may have gone after large prey, such as the amphibious mammal Coryphodon, a creature about the size of a cow and similar to a modern tapir. The relatively short legs and heavily built body mean that Pachyaena were built more for endurance than speed in running, and may have hunted faster prey by running the animal down and attacking when the animal lost stamina from exhaustion.
Sources: Paleocene
Mammals of the World
Postcranial skeleton of the Early Eocene Mesonychid
Pachyaena (Mammalia, Mesonychia)
Maureen A. O'Leary and Kenneth D. Rose, Journal of
Vertebrate Paleontology, 1995, 15(2):401-430
Fossil Butte
National Monument