异齿亚目（Anomodontia）又名缺齿亚目、异齿龙亚目，是兽孔目的三个主要演化支之一，从二叠纪繁盛到三叠纪，可能还继续存活到白垩纪早期。牠们大多数为缺少牙齿的草食性动物。

在二叠纪中期，异齿亚目已呈现多样性，包括：文努科维亚兽科（Venyukoviidae）、奔龙兽下目（Dromasauria）、二齿兽下目，还有早期的原始物种，包括异头兽（Anomocephalus）与Patranomodon。其中只有二齿兽类存活到二叠纪晚期，而且成为晚二叠纪的最成功、大量的草食性动物，在生态位上占据从大型到小型草食性动物的位置。只有少数二齿兽类在二叠纪-三叠纪灭绝事件之后存活下来，其中一科叫水龙兽科，后来发展出肯氏兽科。这些后来出现的动物，是大型、笨重、喙状嘴的动物，依然成为陆地上优势的草食性动物。直到晚三叠纪，当时逐渐改变的环境（也许是逐渐的干燥）造成牠们衰落，最后灭亡，生态位被蜥脚形亚目恐龙所取代。在澳洲的白垩纪早期地层，发现可能属于异齿亚目的化石纪录。

Anomodontia is an extinct group of non-mammalian therapsids containing many species from the Permian and Triassic periods (possibly continuing into the Early Cretaceous), most of which were toothless herbivores. Anomodonts were very diverse during the Middle Permian, including primitive forms like Anomocephalus and Patranomodon and groups like Venyukovioidea, Dromasauria, and Dicynodontia. Of these, only the dicynodonts survived beyond the Middle Permian. Dicynodonts became the most successful and abundant of all herbivores in the Late Permian and Triassic, filling ecological niches ranging from large browsers down to small burrowers. Few dicynodont families survived the Permian–Triassic extinction event, but one lineage evolved into large, stocky forms that remained the dominant terrestrial herbivores right up until the Late Triassic, when changing conditions caused them to decline.