兽齿类（Theriodontia）是兽孔目的第三个主要演化支，生存在二叠纪中期到白垩纪中期。在传统的林奈分类法里，兽齿类是似哺乳爬行动物的一个亚目。在亲缘分支分类法理，兽齿类不仅包括传统的兽齿类，还有牠们的哺乳类后代（以亲缘分支分类法的话，兽脚亚目恐龙也包括了鸟类次演化支）。

兽齿类跟异齿亚目几乎同时在二叠纪中期出现，接近约2亿6500万年前。与同时代的恐头兽亚目与异齿亚目相比，这些早期兽齿类更类似哺乳类。

兽齿类主要分为三类：丽齿兽亚目、兽头亚目、犬齿兽亚目。早期兽齿类可能已经是温血动物。早期物种都是肉食性动物，但在三叠纪几个族群演化成草食性动物。

Theriodonts ("Beast Tooth", referring to more mammal-like teeth), are a major group of therapsids. They can be defined in traditional, Linnaean terms, in which case they are a suborder of mammal-like reptiles that lived from the Middle Permian to the Middle Cretaceous, or in cladistic terms, in which case they include not only the traditional theriodonts but also their descendants the mammals as well (in the same way that, cladistically speaking, the theropod dinosaurs include the birds as a sub-clade).