Washington, June 9 : Paleontologists have, for the first time, found fossilized burrows of land vertebrates in Antarctica, which date back to about 245 million years.
Discovered by researchers from the University of Washington (UW), the burrows belong to tetrapods, which basically are any land vertebrates with four legs or leglike appendages, dating from the Early Triassic epoch.
The fossils were created when fine sand from an overflowing river poured into the animals' burrows and hardened into casts of the open spaces.
The largest preserved piece is about 14 inches long, 6 inches wide and 3 inches deep.
No animal remains were found inside the burrow casts, but the hardened sediment in each burrow preserved a track made as the animals entered and exited.
"In addition, scratch marks from the animals' initial excavation were apparent in some places," said Christian Sidor, a University of Washington assistant professor of biology, who is the lead author of a paper describing the find.
"We've got good evidence that these burrows were made by land-dwelling animals rather than crayfish," he added.
According to Sidor, though fossils of tetrapod bones from later in the Triassic period have been found in a section of Antarctica called Victoria Land, the fossil burrows predate those bone fossils by at least 15 million years.
The fossilized burrows were collected in 2003 and 2005-06 from the Fremouw Formation at Wahl Glacier and from the Lashly Formation at Allan Hills, both toward the outer edges of Antarctica.
Despite the absence of fossil bones, the burrows' relatively small size prompted Sidor to speculate that their owners might have been small lizardlike reptiles called Procolophonids or an early mammal relative called Thrinaxodon.
At the time the burrows were dug, Antarctica would have been ice-free.
However, temperatures still would have been quite cold, since both areas where the burrows were found are within the Antarctic Circle and so experience at least one day a year of complete darkness.
"We have documented that tetrapods were burrowing, making dens in Antarctica, back in the Triassic," said Sidor. "There are lots of good reasons for burrowing at high latitudes, not the least of which is protection from the elements," he added.