Unlike its modern counterpart, Hyaenodon was top dog.

Unlike is modern day relatives, Hyaenodon gigas was the dominant predator of its day. As big as a small rhino, it was the largest of its kind. Fossil evidence shows that even the mighty sabre-toothed cats fell victim to Hyaenodon. Hyaenodon is very well portrayed in Walking with Beasts by BBC.
Hyaenodon was fast,agile and had bone crunching-teeth making it a lethal hunter capable of eating every part of its prey including the teeth! It was most likely a nocturnal hunter that attacked the young or weak and may have gathered in packs to take down larger prey such as the giant pigs Dinohyus and Entelodon.