A relative of Cynognathus, Massetognathus was a plant-eating cynodont belonging to the Traversodontid family. This cynodont lived in what is now South America, in Brazil (paleorrota) and Argentina (Los Chañares Formation) during the Middle Triassic period (220 million years ago).

 Massetognathus was about 50 centimetres (1.6 ft) long. It had cheek teeth specially adapted to chewing on vegetation. It still had the distinctive long snout of its cynodont relatives, with nipping incisors and fang-like canines, but its cheek teeth were not pointed. Instead they were flat-topped and were covered with a number of low ridges, which made them good for grinding any stems, roots and other plant materials. Massetognathus had clawed feet and a long dog-like tail. Like most of its cynodont relatives, it may have been covered in hair.

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