September 13, 2008

Tissue Found in Dino Fossil May Be Biofilm

By Perkins, Sid

New study questions analyses of T. rex remains Three years ago, a team of scientists rocked the paleontology world by reporting the recovery of flexible tissue resembling blood vessels from a 68- million-year-old dinosaur fossil. Now, another group suggests that such pliable material could be something more mundane: a modern-day film of bacterial slime.

The techniques used to assess such pliable materials are new to paleontologists, comments Matthew T. Carrano of the Smithsonian Institution in Washington, D.C. "It will take a while for paleontologists to sort through the arguments," he adds.

After dissolving and analyzing parts of a fossilized Tyrannosaurus rex leg bone, scientists - including Mary H. Schweitzer, a paleontologist at North Carolina State University in Raleigh - reported in 2005 (SN: 3/26/05, p. 195) that the fossil contained small bits of collagen, a fiber-forming protein that's the largest non-mineral component of bone.

But analysis of other fossils now suggests that soft tissue in fossil bones could just as likely be modern contamination.

Rather than dissolving fossil fragments and analyzing the residue, Thomas G. Kaye, a paleontologist at the University of Washington's Burke Museum of Natural History and Culture in Seattle, and his colleagues cracked open dozens of old bones to see whether soft tissue was visible. Some of the specimens were 65 million years old and from the same rock formation as the T. rex that Schweitzer and her colleagues studied.

Kaye and his colleagues suggest in the July 30 PLoS ONE that the small, bloodcell-like spheres in the bones they studied are tiny enigmatic structures called framboids, named for the French word for raspberry. Framboids are typically made of iron sulfides, but those riddling the fossils analyzed by Kaye's team - as well as Schweitzer's team in the T. rex leg bone - were instead made of iron oxide.

A variety of evidence suggests that pliable material found in fossils may be biofilms of modern-day bacteria rather than ancient cells and blood vessels. Many of the fossils analyzed by Kaye and his colleagues contained such material. Carbondating analyses of some samples indicate that the material is very recent, forming after 1950, Kaye says.

Recent studies, Kaye's team reports, also show that some bacteria sport a collagen-like surface protein, which might trick a biochemical test designed to detect collagen.

Schweitzer and her colleagues take issue with the findings. "There really isn't a lot new here, although I really welcome that someone is attempting to look at and repeat the studies we conducted," she notes.

Schweitzer and her team dismissed bacterial biofilms as a cause of the tissues she and her team observed. Such coatings probably would be thicker along the lower surfaces of the vascular spaces, but the flexible structures her team recovered had walls with an even thickness, she says. Also, there's no reported evidence that biofilms can produce branching, hollow tubes like those noted in her study.

Furthermore, says John M. Asara, an analytical chemist at Harvard Medical School in Boston and a colleague of Schweitzer's, the type of collagen found was bone-specific and isn't a common protein contaminant.

Nevertheless, the interpretation that the soft tissue in fossils is actually modern-day biofilms "is a reasonable alternate hypothesis," Carrano says.

Biofilms (shown by arrows) peel from vascular canals in fossil dinosaur bone.

Copyright Science Service, Incorporated Aug 30, 2008

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