Lystrosaurus

Lystrosaurus is an extinct genus of herbivorous dicynodont therapsid from the late Permian and Lower Triassic epochs (about 250 million years ago). 
It lived in what is now Antarctica, India, China, Mongolia, Russia and South Africa. Four to six species are known. They ranged in size from that of a small dog to 2.5 meters long.
"Lystrosaurus" survived the Permian-Triassic extinction event, 252 million years ago. In the Lower Triassic, they were the most common terrestrial vertebrates. In some fossil beds they make up as many as 95% of the individuals. Researchers have offered various ideas for why they survived the extinction and thrived in the early Triassic.