Cynognathus (Greek for "dog jaw"), mammal-like reptile of the order Therapsida (see Therapsid) that lived in South Africa and South America in the middle Triassic Period (about 231 million to 213 million years before present). Cynognathus was a carnivorous (meat-eating) member of the cynodonts with a long body and slender limbs. Cynodonts were a carnivorous suborder of therapsids, the group of mammal-like reptiles that also included the herbivorous (plant-eating) dicynodonts. Cynognathus looked like a dog and was a formidable predator with its long snout and powerful jaws set with short nipping incisors and sharp stabbing canines. Cheek teeth with multiple points were located behind the canines and were used to slice and shred the flesh of prey. The main prey of Cynognathus was Kannemeyeria, a 3 m (10 ft) long dicynodont (a group of herbivorous therapsids) that had only two canine teeth in the front of its large beak. Cynognathus also hunted other dicynodonts.
Most cynodonts and all dicynodonts became extinct at the end of the Triassic Period. Changes in the plant life of that time are thought to have contributed to the extinction of the cynodont and dicynodont herbivores. That would have caused the cynodont carnivores, such as Cynognathus, who preyed on these herbivores, to starve and die. Cynognathus's relatives, primitive mammals that evolved from their therapsid ancestors, survived the Triassic extinction.