鬣齿兽（Hyaenodon），又名肉齿兽，或称熊狗。是鬣齿兽科已灭绝的一类。其下的一些物种是大型陆上肉食性哺乳动物的一员。

鬣齿兽是高度专化的掠食者，于4100万年前的始新世晚期出现，直至2100万年前的渐新世仍然存在。牠们窄长的颚部强而有力，很适合咬紧及咬碎东西。牠们的头颅骨很巨型，但脑部却很细小。牠的长头颅骨上有很窄的吻，比较犬科的吻算是较大。牠的颈部较头颅骨短，身体则长及粗壮，有很长的尾巴。前脚及后脚上都有五趾，第一趾比其他的脚趾较短。

从鬣齿兽的头颅骨可知牠们有敏锐的嗅觉。一些物种可能专门是吃腐肉的，但其他的明显是主动的掠食者。鬣齿兽外观很像现今的鬣狗，但有更尖锐的牙齿及良好发长的裂齿，故可见牠们有不同的食性。鬣齿兽不会吃腐肉，但会猎食如羊般大小的有蹄类。

Hyaenodon ("hyena-tooth") is the type genus of Hyaenodontidae, a group of extinct carnivorous fossil mammals from Eurasia, North America and Africa, with species existing temporally from the Eocene until the middle Miocene, existing for approximately 26.1 million years. The various species of Hyaenodon competed with each other and with other hyaenodont genera (including Sinopa, Dissopsalis and Hyainailouros), and played important roles as predators in ecological communities as late as the Miocene in Africa and Asia. Species of Hyaenodon have been shown to have successfully preyed on other large carnivores of their time, including a "false saber-tooth cat", Dinictis by analysis of tooth puncture marks on a fossil Dinictis skull in North Dakota .