Pareiasaurs were large, heavy animals, about two to ten feet in length with stocky arms and legs, small heads, leaf-shaped teeth, and bony knobs covering their heads and bodies.
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Pareiasaur means “cheek lizard,” and some scientists theorize they may be the ancestors of turtles. The various species are believed to have weighed up to 1,300 pounds. Notably, pareiasaurs were most likely the first large herbivores on Earth. Given what scientists have recreated their physical appearance to look like, pareiasaurs have been considered the “ugliest fossil reptiles.”
Pareiasaurs met their end in the largest mass extinction event to date, the Permian–Triassic extinction event, which occurred about 252 million years ago.
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The pareiasaurs, which lived for some ten million years during the Permian period, were wiped out along with 70% of all land organisms and 90-96% of all marine species. Likely caused by an impact event, volcanism, or sudden and lethal amounts of methane, the Permian–Triassic extinction event is known as the Great Dying, and recovery of life may have taken as much as 10 million years to get back on track.