爪兽（学名 Chalicotherioidea） 是一类已经灭绝了的古哺乳动物，属于奇蹄目。跟马的亲缘关系非常近，面部轮廓也酷似马，但是不长蹄而长爪，且不善奔跑。爪兽的前肢较后肢长，这样的形体看上去像现代的鬣狗。爪兽行走的时候用指节着地，这又让它看上去像大猩猩。爪兽以树叶和草根为食。由于牙齿是低冠牙，所以不能吃草。

爪兽是动物进化史上的另类物种，体现在如下方面：

爪兽在更新世就绝灭了。但是现在却有人怀疑非洲传说中的喃迪熊(Nandi Bear)是爪兽在非洲丛林中的孑遗。

Ancylopoda is a group of browsing, herbivorous, mammals in the Perissodactyla that show long, curved and cleft claws. Morphological evidence indicates the Ancylopoda diverged from the tapirs, rhinoceroses and horses (Euperissodactyla) after the Brontotheria, however earlier authorities such as Osborn sometimes considered the Ancylopoda to be outside Perissodactyla or, as was popular more recently, to be related to Brontotheria.