Lystrosaurus is herbivorous genus of Late Permian and Early Triassic Period dicynodont therapsids, which lived around 250 million years ago in what is now Antarctica, India, and South Africa. Four to six species are currently recognized, although from the 1930s to 1970s the number of species was thought to be much higher. They ranged in size from a small dog to 2.5 meters long.
Lystrosaurus was a dicynodont therapsid, between 0.6 to 2.5 m (2.0 to 8.2 ft) long with an average of about 0.9 m (3.0 ft) depending upon the species.
Unlike other therapsids, dicynodonts had very short snouts and no teeth except for the tusk-like upper canines. Dicynodonts are generally thought to have had hornybeaks like those of turtles, for shearing off pieces of vegetation which were then ground on a horny secondary palate when the mouth was closed. The jaw joint was weak and moved backwards and forwards with a shearing action, instead of the more common sideways or up and down movements. It is thought that the jaw muscles were attached unusually far forward on the skull and took up a lot of space on the top and back of the skull. As a result, the eyes were set high and well forward on the skull, and the face was short.
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