Scientists find 245 million-year-old burrows of land vertebrates in ...( For the first time paleontologists ...)

For the first time paleontologists have found fossilized burrows of tetrapods any land vertebrates with four legs or leglike appendages in Antarctica dating from the Early Triassic epoch, about 245 million years ago.

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 and curator of vertebrate paleontology at the Burke Museum of Natural History and Culture at the UW.

"We've got good evidence that these burrows were made by land-dwelling animals rather than crayfish," said Sidor, who is lead author of a paper describing the find, which is being published in the June edition of The Journal of Vertebrate Paleontology.

Co-authors are Molly Miller, a geology professor at Vanderbilt University, and John Isbell, a geosciences professor at the University of Wisconsin-Milwaukee. The work was funded by the National Science Foundation.

Fossils of tetrapod bones from later in the Triassic period have been found in a section of Antarctica called Victoria Land, but the fossil burrows predate those bone fossils by at least 15 million years, Sidor said.

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 P
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