Diarthrognathus broomi A species of mammal-like reptiles, recorded from the Triassic, that is one of the closest to mammalian ancestry. It is assigned to the Ictidosauria and is characterized by a number of advanced cranial features, including the co-occurrence of the older reptilian (quadrate—articular) and newer mammalian (squamosal—dentary) jaw joints. The skull is only 4–5 cm long and its dentition is not as specialized as that of certain other mammal-like reptiles from the Upper Triassic.

Diarthrognathus broomi Of the many mammal-like reptiles (see SYNAPSIDA) recorded from the Triassic, this species is one of the closest to mammalian ancestry. It is assigned to the Ictidosauria and is characterized by a number of advanced cranial features. The skull of Diarthrognathus is only 4–5 cm long and its dentition is not as specialized as that of certain other mammal-like reptiles from the Upper Triassic.