In 2005, Burke curator of vertebrate paleontology Christian Sidor led an expedition to Antarctica to learn about what types of plants and animals on the icy continent before the age of dinosaurs. The results were surprising. In 2008, Sidor and his colleagues published a paper documenting 245 million year old fossilized burrows of land-living vertebrates (or tetrapods) from Antarctica. No skeletal remains were found inside the 6-inch wide by 3-inch deep burrow casts, but the hardened sediment in each burrow preserved a track made as the animals entered and exited. Fossilized burrows, some containing tetrapod bones, have previously been recorded in rocks of the same age in South Africa and those burrows are nearly identical to the fossils unearthed in Antarctica. The small size of the burrows suggested that their makers might have been small lizard-like reptiles called procolophonids or an early mammal relative called Thrinaxodon.
During the Triassic Period, Antarctica and South Africa were connected as part of a supercontinent called Pangea. At the time the burrows were dug, Antarctica was probably ice-free but temperatures still would have been quite harsh, since even 245 million years ago the burrows were found at a latitude within the Antarctic Circle (and so experienced at least one full day of complete darkness).