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 had hair, but not a full fur.