兽孔目（学名：Therapsida）是合弓纲中的一目。传统上，单孔亚纲被归类于爬行纲的一个亚纲，并名为似哺乳爬行动物。然而单孔亚纲现在为独立的合弓纲，是蜥形纲的姐妹分类单元，较接近哺乳动物。在亲缘分支分类法中，兽孔目通常包括哺乳类，哺乳类是犬齿兽类的后代。现代哺乳动物的许多特征，例如毛发、乳腺、直立的四肢姿势，都演化自早期兽孔类动物。

在约2亿7500万年前，盘龙目（楔齿龙科）演化出兽孔类。目前已发现最早的兽孔类动物，是二叠纪晚期的四角兽。在二叠纪中期，兽孔类取代盘龙目，成为优势陆地脊椎动物。在三叠纪中期，多样性的主龙类动物取代兽孔类，成为优势陆地脊椎动物，少数二齿兽类仍保持多样性、存活到三叠纪晚期。在约2亿2500万年前，犬齿兽类演化出现代哺乳动物的祖先。

Therapsida is a group of synapsids that includes mammals and their ancestors. Many of the traits today seen as unique to mammals had their origin within early therapsids, including having their four limbs extend vertically beneath the body, as opposed to the sprawling posture of other reptiles. The earliest fossil attributed to Therapsida is Tetraceratops insignis from the Lower Permian. Therapsids evolved from pelycosaurs (specifically sphenacodonts) 275 million years ago. They replaced the pelycosaurs as the dominant large land animals in the Middle Permian and were replaced, in turn, by the archosauromorphs in the Triassic, although one group of therapsids, the kannemeyeriiforms, remained diverse in the Late Triassic. The therapsids included the cynodonts, the group that gave rise to mammals in the Late Triassic around 225 million years ago. Of the non-mammalian therapsids, only cynodonts and dicynodonts survived the Triassic–Jurassic extinction event. The last of the non-mammalian therapsids, the tritylodontid cynodonts, became extinct in the Early Cretaceous, approximately 100 million years ago.