作为岛上一种锲而不舍的群体狩猎种群，鬣齿兽栖息于山脉与苔原地区，通常是三五成群一同行动。这是一种非常聪明的掠食者，在行动之前，它们会权衡战斗的得益是否值得赌上受伤的风险。 鬣齿兽通常避免战斗，除非附近有虚弱的猎物，或是新鲜的尸体。这种性情切换相当迅速，当附近出现受伤或是垂死的生物时，鬣齿兽会迅速变得极具攻击性，采用非常冷酷的群体攻击手段。 在大嚼猎物的生肉时，鬣齿兽能够快速回复生命值和耐力值。
Common name: Hyaenodon
Species: Hyaenodon dirus
Time: Late Eocene-Early Miocene
Among the Island's most tenacious pack is Hyaenodon dirus, a carnivore most often found across the mountains and tundras in packs of 3 to 6. The Hyaenodon is a very intelligent predator. Before engaging, it determines if the payoff for a fight is worth the risk of injury. Hyaenodon often prefers not to fight unless there is already weakened prey or a fresh carcass nearby. This temperament changes quickly, though, near the presence of injured creatures. Hyaenodon quickly becomes very aggressive... ...and the pack attacks with ruthless abandon. With each vicious chomp of scavenged meat, the Hyaenodon rapidly recovers health and stamina.
Despite being too small to ride, Hyaenodon are still popular pets. Their intelligence means they train well, and their natural pack mentality makes them excellent hunting dogs. Their ability to quickly recover health by consuming raw flesh off the bone ensures they can take punishment yet continue to fight, and they can efficiently preserve meat in specially-crafted saddle-bags. A common (and terrifying) sight on the tundra is a rider on a Canis with a pack of Hyaenodon at its side, howls and jeers echoing through the night.