Diadectes (meaning crosswise-biter) is an extinct genus of large reptiliomorphs or synapsids[1] that lived during the early Permian period (Artinskian-Kungurian stages of the Cisuralian epoch, between 290 and 272 million years ago).

At the same time, its teeth show advanced specialisations for an herbivorous diet that are not found in any other type of early Permian animal.

The broad, blunt cheek teeth show extensive wear associated with occlusion, and would have functioned as molars, grinding up the food.

Though very similar, they would be analogous rather than homologous to those of early amniotes such as pelycosaurs and pareiasaurs, as the first reptiles evolved from small, swamp-dwelling animals like Casineria and Westlothiana.

[8] Diadectes was first named and described by American paleontologist Edward Drinker Cope in 1878,[9] based on part of a lower jaw (AMNH 4360) from the Permian of Texas.

Diadectes fossil remains are known from a number of locations across North America, especially the Texas Red Beds (Wichita and Clear Fork).

[10] Below is the cladogram from Kissel's thesis: Limnoscelidae Tseajaiidae Ambedus pusillus Oradectes sanmiguelensis Orobates pabsti Desmatodon hesperis Silvadectes absitus Diadectes tenuitectus Diadectes sideropelicus Diasparactus zenos However, according to the ICZN, a name presented in an initially unpublished thesis such as Kissel's is not valid.