Researchers believe the burrows provided much needed shelter for the mammal-like Thrinaxodon.
"When it's very cold or even when it's very hot outside, burrows seem to maintain a relatively even temperature," Sidor said.
But finding Antarctic burrows that contain ancient animal remains is very difficult, in part because fossilized bones are most often found inside rocks.
Antarctica today contains more glaciers and ice than exposed rock.
"Without rocks, there's no way you're going to find bones," Sidor said.
"Rock outcrops—the places for us to search—are very remote and very limited, which makes anything found in Antarctica a tremendous discovery."
Paleontologists in South Africa have found similar burrows from the same time period containing tetrapod remains.
"The same types of animals lived in South Africa as in Antarctica," Sidor said, "so we expect the burrows to be similar."
Preparation and Luck
Anthony Martin is a paleontologist at Emory University in Atlanta who was not involved with the study.
"Burrows give a major survival advantage to whoever is living in them," Martin said.
(Related: "Digging Dinosaur Discovered Inside Fossil Den" [March 21, 2007].)
"So there were good reasons for why Mesozoic animals were burrowing to avoid freezing temperatures outside the burrow, all while getting away from predators or safely raising their young."
According to Martin, fossil burrows are much more common than most geologists and paleontologists realize.
But pinpointing them requires knowing what they look like and precisely where to look.
"Fortunately these paleontologists had the ideal combination of preparation and luck on their side, which worked out very well for them," Martin said.
"After all, you can't go to Antarctica just any time you feel like it and then go searching for fossil tetrapod burrows!"
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