犬齿兽亚目是兽孔目的一类。它们是兽孔目中最多样性的其中一群。它们以类似狗的牙齿命名。

犬齿兽类拥有几乎所有哺乳类的特征。牠们的牙齿全部分化，脑壳往头后方突起，多数以直立的四肢行走。犬齿兽类仍然卵生，就像所有中生代原始哺乳类一样。牠们的颞颥孔远比牠们祖先的大，较宽的颧弓支称强壮的下颌肌肉，证实更像哺乳类的头骨。牠们也有除了兽头类以外兽孔目所缺乏的次生颚，兽头类与犬齿兽类有亲近的血缘关系。它们的犬齿是牠们下颌的最大骨头，其他的小骨头移动到内耳。牠们可能是温血动物，覆盖着毛发。

The cynodonts ("dog teeth"), in the clade Cynodontia, are therapsids that first appeared in the Late Permian (approximately 260 Ma). The group includes modern mammals (including humans) as well as their extinct ancestors and close relatives. Nonmammalian cynodonts spread throughout southern Gondwana and are represented by fossils from South America, Africa, India, and Antarctica. In the northern continents, fossils have been found in eastern North America as well as in Belgium and northwestern France. Cynodontia is one of the most diverse groups of therapsids.