Hyaenodon

Hyaenodon ("hyena-tooth") is an extinct genus of carnivorous placental mammals from the tribe Hyaenodontini, part of the subfamily Hyaenodontinae (which is within the family Hyaenodontidae), that belonged to the now extinct order Hyaenodonta. The genus was found lived in Eurasia and North America from the Middle Eocene to the Late Miocene, from 38 to 11.4 million years ago, existing for 26.6 million years. Hyaenodon was thought to have evolved in Asia, probably evolving from Propterodon. The genus currently consists of at least 40 species, although due to sexual dimorphism and intraspecific variation, there were likely fewer species within the genus. The species within the genus ranged in size from H. filholi, which weighed 2 kg (4 lb 7 oz), to H. gigas and H. mongoliensis, which were estimated to be similar in size to Hyainailouros. Smaller species, such as H. microdon, were mesopredators, having to compete with contemporary small carnivorans. On the other hand, the largest species were likely the apex predators of their time, hunting large herbivores of their environments. Fossil records also suggests they were also capable of hunting smaller predators. Several species within the genus were cursorial predators, either being ambushing or pounce-pursuit predators. The canines of the animal mediolaterally compressed much like canids, landing shallow bites on their prey. Unlike canids such as wolves, they are thought to have been solitary predators. The genus saw a decline during the Late Eocene to Early Oligocene, with only a few species being present in the Miocene. Many experts hypothesize their decline and extinction was the result of competition with carnivorans. Although, this hypothesis has been challenged over the recent years. With many experts instead hypothesizing the cause of their decline and eventual extinction was the inability to adapt to open environments.