Christian Sidor at work (Image: Cara Fritz/Oregon State University) The location of the burrow

Long before the age of the dinosaurs, something was constructing tunnels in Antarctica.

A burrow has been discovered in the ancient flood plain of a broad Antarctic river only a few million years after a mass extinction ended the Permian period.


The tunnel was preserved when a flood washed sand into it, forming a cast 35 centimetres deep and 16 cm wide – and even preserving claw marks scratched into the walls during excavation.

Palaeontologist Christian Sidor of the University of Washington thinks the den belonged to Thrinaxodon, a small badger-like reptile closely related to mammals.

A second candidate is a lizard-like reptile called Procolophon. Bones of both animals have been found in Antarctica and in South Africa.

Winter slumber

Fossils show that insects and plants prospered all over late-Permian Antarctica, but the oldest known fossils of four-legged animals come from sites in the Transantarctic Mountains where Sidor found the burrow.

Four-legged animals had spread over other continents tens of millions of years earlier, but were late to arrive in Antarctica, which was part of the vast supercontinent of Pangea, and like today was near the south pole.

The 245-million-year-old structure is the oldest known evidence of quadrupeds in Antarctica, and shows that, like some contemporary animals, they liked to settle down for a long winter’s nap.

Extreme environment

In the late Permian, Antarctica had a more moderate climate than that encountered today, but it was still a pretty extreme environment.

“Temperatures within a burrow remain much more constant than outside,” says study co-author Molly Miller of Vanderbilt University in Nashville, Tennessee, US. So the dark of polar midwinter would have been a perfect time to snuggle deep in the burrow for a long nap.

While the find is exciting, even older fossils may be hidden under the ice that now covers most of the continent, Sidor says.

Journal reference: Journal of Vertebrate Paleontology (vol 28, p277)