中爪兽（Mesonyx），又名中兽或钝肉齿兽，是中爪兽科下的一类。牠们外表像狼及大小如狗，是始新世中期（约4500万年前）美国怀俄明州及东亚的掠食者。牠的四肢灵活，相信是奔跑的能手，可能捕食草食性的有蹄类。不过中爪兽并没有爪，趾上有细小的蹄。头颅骨很长，脑壳上有相对较大的矢状嵴，可以连接大的颚部肌肉，增强咬劲。

中爪兽属下的Mesonyx uintensis是在怀俄明州发现，颅骨长约42.9厘米，而面长20.6厘米。Mesonyx uintensis的另一个标本是来自犹他州北部。

Mesonyx ("middle claw") was a wolf-like mammal of the family Mesonychidae, the type family of the order Mesonychia (sometimes referred to by its older name, "Acreodi"), existing 51.8—51.7 Ma (AEO).

Mesonyx measured about 1.5 m (5 ft) long not including the tail, and weighted an estimated 22.7–34 kg. It was a fast predator from the Middle Eocene of Wyoming, and it probably hunted hoofed plant eaters, moving lightly on its toes. However, instead of claws, Mesonyx's toes ended in small hooves. Its long skull had a relatively large sagittal crest above the braincase to anchor large jaw muscles and give it a powerful bite.