Claim: Different Hyaenodon species varied highly in size and weight.
Evidence: Some species of this genus were among the largest terrestrial carnivorous mammals of their time; others were only of the size of a marten. The average weight of adult or subadult H. horridus, the largest North American species, is estimated to about 40 kg (88 lb) and may not have exceeded 60 kg (130 lb). H. gigas, the largest Hyaenodon species, was much larger, being 378 kg (833 lb) and around 10 feet (3.0 m). H. crucians from the early Oligocene of North America is estimated to only 10 to 25 kg (22 to 55 lb). H. microdon and H. mustelinus from the late Eocene of North America were even smaller and weighed probably about 5 kg (11 lb).