They had long skulls, slender jaws, slim bodies, and a tendency to walk on their toes rather than flat-footed (plantigrade). They ranged in size from 30 to 140 cm at the shoulder. "Hyaenodon gigas", the larger species, was as much as 1.4 m high at the shoulder, 10 feet long and weighed about 500 kg, but most were in the 5–15 kg range, equivalent to a mid-sized dog. Fossil evidence of their skulls shows that they had a particularly acute sense of smell, while their teeth were adapted for slicing, rather than crushing.