Hyaenodon, extinct genus of carnivorous mammals that first appeared in the fossil record about 42 million years ago during the middle of the Eocene Epoch and persisted until about 25 million years ago near the end of the Oligocene Epoch. The genus, in the order Creodonta, contained about 30 species. Hyaenodon was a large and efficient predator; its skull was long and narrow, with large, catlike teeth. The body of Hyaenodon was more doglike, however, and the animal would have been similar to the recently extinct Tasmanian wolf, Thylacinus.