Cynognathus is an extinct genus of large-bodied cynodontian therapsids that lived in the Middle Triassic.

[4] Possible autapomorphies of C. crateronotus include an extremely elongated postorbital bar and sectorial postcanine teeth with two serrated cusps distal to a recurved apex.

In 1889, near Lady Frere, at a location where earlier Alfred Brown had discovered a tooth, Seeley excavated a skull and partial postcranial skeleton of a cynodontian.

[6] The generic name Cynognathus is derived from Ancient Greek kyon and gnathos, meaning "dog jaw".

Cynognathus crateronotus in a cladogram after Stefanello et al. (2023):[12] Cynognathus crateronotus Diademodon tetragonus Langbergia modisei Trirachodon berryi Sinognathus gracilis Pascualgnathus polanskii Luangwa drysdalli Scalenodon angustifrons Mandagomphodon hirschoni Massetognathus pascuali Exaeretodon argentinus In the Karoo Basin in what is now South Africa, Cynognathus lived in open environments with warm, dry summers and cool, wet winters, similar to today's Western Cape region but more arid.

All these adaptations are consistent with maintaining a regular, high basal metabolic rate ("warm-blooded"), as in modern mammals.

The possible lack of belly ribs, in the stomach region, suggests the presence of an efficient diaphragm, an important muscle that allows mammals to breathe equally well when they are walking, running, or holding still.