Size and Weight:
About the size and weight of a smallish pig, Lystrosaurus was a classic example of a dicynodont ("two dog toothed") therapsid--the "mammal-like reptiles" of the Triassic period that preceded the dinosaurs, lived alongside the archosaurs (the dinosaurs' true ancestors), and eventually evolved into the earliest mammals of the Mesozoic Era.
The most amazing thing about Lystrosaurus is how widespread it was. Remains of this ancient reptile have been unearthed in India, South Africa and even Antarctica (these three continents were once merged together in the giant continent Pangea), and its fossils are so numerous that they account for 95 percent of the bones recovered at some fossil beds. The famous evolutionary biologist Richard Dawkins has called Lystrosaurus the "Noah" of the Permian/Triassic boundary, being one of the few creatures to survive this little-known global extinction event.
By the way, it was once thought that Lystrosaurus lived much like a modern hippopotamus, pursuing a semi-aquatic existence, but it now appears that this creature thrived in hot, dry environments--perhaps an adaptation that aided its success in the harsh climate of the early Triassic period.