In giraffes, these bumps help to distinguish males from females, since only females have obvious tufts of fur on theirs. They also help to protect the heads of males during combat, which is one reason why the bumps are usually hairless on males. Over time, the hair and skin on them wears away. Perhaps the bumps held similar functions in pareiasaurs.
Since Bunostegos had characteristics of even earlier reptiles, the researchers think a population of these cow-sized reptiles persisted in the supercontinent, essentially isolated, for millions of years.
"Our work supports the theory that central Pangea was climatically isolated, allowing a unique relict fauna to persist into the late Permian," said co-author Christian Sidor, also from the University of Washington.
This is surprising, he said, because areas outside the central Pangea region show fossil evidence of regular faunal interchange back in pre-dino times.
Paleontologist Gabe Bever, who was not involved with the study, said, "Research in these lesser-known basins is critically important for meaningful interpretation of the Permian fossil record. Our understanding of the Permian and the mass extinction that ended it depends on discovery of more fossils like the beautifully bizarre Bunostegos."