Break a fossil, look what you learn

A maverick scientist finds possible blood vessels in a T. rex bone, a discovery that could unlock many mysteries of dinosaurs

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By William Mullen
Tribune staff reporter

March 25, 2005

Dissolving away the minerals in a 3-inch chunk of fossilized dinosaur bone, a North Carolina paleontologist has found what appear to be intact, still-soft blood vessels and blood cells belonging to a 68 million-year-old Tyrannosaurus rex.

Something of a scientific maverick, Mary Schweitzer said she hopes to complete further tests by summer's end that might confirm that the flexible, "stretchy" material she recovered from the bone is actual preserved tissue from the dinosaur.

If she can confirm it, her method of investigation is likely to revolutionize paleontology. Such tissues might yield actual dinosaur DNA, for example. The blood vessels and cells also could provide important information on whether dinosaurs were warm- or cold-blooded, offering new insights into how they lived.

A paleontologist at North Carolina State University, Schweitzer reports her findings in Friday's edition of the journal Science.

"It's very exciting," Schweitzer said in a telephone interview Thursday, "but it's only a beginning. There is much, much more very expensive work to do, and there are only two of us working on it right now, myself and my technician, Jennifer Wittmeyer.

"They look like blood vessels and act like blood vessels. Now we have to do molecular and chemical analysis of them to see if they are cells or simply [non-organic] geological artifacts. In order to say they are cells, we have to see if they have cell components."

Schweitzer's research methods seem to upend accepted theories of fossilization. Conventional wisdom suggests that when animals like dinosaurs died millions of years ago and were covered in silty mud, inert earth minerals gradually seeped into bony tissues and replaced all organic material. The minerals transformed the bone into fossil rock, supposedly destroying any soft tissue.

Her findings, if confirmed, promise an explosion of new information, said University of Chicago paleontologist Paul Sereno. Schweitzer is studying dinosaur bone material at the subcellular level, he noted, an area where little previous research has been done.

"I think it is just amazing work," Sereno said.

In an era when most paleontologists go to extraordinary lengths to develop new, non-destructive ways to study fossilized bones, Schweitzer for several years has sought out fossils she could destroy by dissolving the mineral content so she could study the residue left behind.

"Most [paleontologists] cringe when they see me coming," Schweitzer said with a laugh, referring to her destructive reputation.

One who hasn't cringed is paleontologist Jack Horner from the Museum of the Rockies in Bozeman, Mont., who had been Schweitzer's thesis adviser as she worked on her doctorate.

Supportive of her experiments in the past, Horner last summer provided the breakthrough specimen she needed.

"His team found a T. rex fossil in Montana," she said, "in a place so remote the fossil had to be helicoptered out. The femur was so big that, once in its field jacket, it couldn't fit on the chopper, so they broke it, and they didn't apply any preservative to the break.

"Jack's always let me look at his broken bones."

Horner supplied her with a section of the bone about 3 inches long, Schweitzer said, and she and Wittmeyer dissolved the minerals in the fossil.

She was hoping her work eventually would allow her to study the microstructure and organic components of dinosaur bone. Bones are made up of proteins and minerals, so removing the minerals from a modern bone leaves behind "supple, soft organic materials," Schweitzer said in a news release.

Most scientists would say that if minerals are removed from a fossil bone, nothing would be left.

But when Schweitzer and Wittmeyer removed the mineral from Horner's T. rex bone, they said they were left with "stretchy bone matrix material that, when examined microscopically, seemed to show blood vessels, osteocytes, or bone building cells, and other recognizable organic features."

Because birds are thought to be living descendants of dinosaurs, Schweitzer compared the tissue found in the T. rex femur with tissues from leg bones of the largest living birds, ostriches. Both samples, she said, had transparent, branching blood vessels, and many microstructures in the T. rex sample looked similar to blood and bone cells from the ostrich.

Schweitzer said she later got similar results from fossil bones of three other dinosaurs, an 80 million-year-old hadrosaur and two 65 million-year-old tyrannosaurs.

"They were all preserved a little bit differently than each other, but they all contained very similar material we found in the T. rex," she said.

Such material might not be found in all dinosaur bones, she said, but finding it in the future may "not be as rare an event as we thought."

Though Sereno said he doubts DNA could be recovered from this kind of material, he said that looking at it on the subcellular level may finally show scientists how and why dinosaurs grew so large physiologically.

Many dinosaur predators grew as large or nearly as large as the 40-foot-long T. rex, he said, but no land mammal predator has grown any bigger than modern polar bears.

"If I was in this line of study, I would get a nice library of bird books and study every bloody thing a bird does at cellular and subcellular level," he said. "They are going to learn a lot."

Most scientists believe it's not possible for organic molecules to be preserved for more than 100,000 years, but Schweitzer said she thinks at least some fragments of original molecular material might still be present in the dinosaur remains she is studying.

"We may not really know as much about how fossils are preserved as we think," she said in the news release.

"Our preliminary research shows that antibodies that recognize collagen react to chemical extracts of this fossil bone. If further studies confirm this, we may have the potential to learn more not only about the dinosaurs themselves, but also about how and why they were preserved in the first place."

Until now, the closest look that scientists have had at soft tissue from dinosaurs has largely been limited to a few fossilized impressions of skin. Schweitzer's article in Science, co-written by Wittmeyer, Horner and Jan Toporski of the Carnegie Institution, could revolutionize future dinosaur research if borne out through subsequent study.

"It has the potential for that," she said, including the possibility of isolating dinosaur DNA as was depicted in the film "Jurassic Park."

"But even if we could get great DNA samples from a dinosaur, we're not going to be able to clone a dinosaur," she said. Any recovered DNA samples would still be too fragmentary to replicate the complete dinosaur genome, she said, and the many other unknown variables, such as chromosomal makeup and developmental needs, would doom any such effort.

More promising, she said, would be new avenues of inquiry that might lead to ways of finding out whether dinosaurs were warm-blooded or determining the sex of individual dinosaur fossil specimens.

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