for National Geographic News
Fossilized burrows found in Antarctica could be the first evidence that four-limbed land animals, or tetrapods, lived in the region as far back as 245 million years ago, paleontologists have announced.
Although no animal remains were discovered, the burrows act as "trace fossils" that reinforce the theory that Antarctica was once ice free and supported a very different array of wildlife than it does today.
The burrows were preserved when sand from a nearby river overflowed into them and hardened, creating casts of the open spaces.
The largest den is only about 6 inches (15.2 centimeters) wide and 14 inches (35.5 centimeters) long.
Based on their size, some of the burrows might have belonged to members of a genus of cat-size mammal relatives known as Thrinaxodon, the scientists say.
"[Thrinaxodon] bones have been found in the Antarctic already," noted lead study author Christian Sidor, a biologist at the University of Washington and curator of vertebrate paleontology at the Burke Museum of Natural History and Culture.
"So we think this is the animal that was making the larger of the two burrows that we describe in the paper."
Sidor's study is set to appear in the June issue of the Journal of Vertebrate Paleontology.
The fossils were collected in 2003 and 2006 toward the outer edges of Antarctica from the Fremouw Formation at Wahl Glacier and from the Lashly Formation at Allan Hills.
During this time, all of Earth's landmasses were joined into a supercontinent called Pangaea, although the regions where the burrows were unearthed were within the chilly Antarctic Circle.
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