A Rex In The Roost

Organic matter recovered from a Tyrannosaurus rex shows a link between the dinosaur and what may be its closest living relative -- the chicken

April 13, 2007|By Erika Gebel | Erika Gebel,Special to The Sun

THE TISSUE SAMPLE

Paleontologists were able to extract bone-making collagen from the thighbone of a 68 million-year-old Tyrannosaurus rex.

WE HAVE A MATCH

Using the collagen extracted from the T. rex?s thighbone, paleontologists determined a link in the collagen material found in the bone and that of a modern-day chicken.

Next time you order fried chicken, consider this: Beneath that crispy skin, you may find a link to the heart of history's most terrifying beast.

New evidence unveiled in today's edition of Science puts the fearsome Tyrannosaurus rex embarrassingly close - in evolutionary terms - to the modern-day chicken.

The research, presented in two scientific papers, focuses on some miraculously preserved soft tissue from the femur, or thighbone, of a 68 million-year-old T. rex recovered from a sandstone bluff in Montana. Before this, the oldest protein scientists have studied was less than 300,000 years old.

"A couple years ago, when we reported [finding] soft tissues, we were greatly surprised, Everyone was." said Mary Schweitzer, a molecular paleontologist at North Carolina State University in Raleigh and an author of both papers.

Normally, fossilized remains like these don't leave many organic clues for researchers. But this tissue had an intricate microscopic structure, which tantalized scientists with the possibility that traces of biologically important molecules, such as proteins, might remain.

"Bone is both mineral and protein," Schweitzer explained, and the most common protein is collagen - which shows up as a long fibrous material that provides strength to bones, tendons, ligaments, cartilage and teeth.

So researchers treated the ancient Tyrannosaurus rex bone with a fluorescent molecule designed to stick specifically to chicken collagen. The resultant green glow proved not only that collagen was there, but also that T. rex collagen must look at least something like that found in chickens.

Just to be certain, scientists applied a collagen-eating enzyme to the femur. This time, when they administered the fluorescent molecule, there was only darkness. What the enzyme devoured must have been collagen.

So what's the big deal? Like bases in DNA, the sequence of amino acids that make up a protein chain can reveal the evolutionary history of its host animal.

For example, a particular protein from a human would have a sequence more like a chimp's than a chicken's. But to get at the sequence of the dinosaur protein, the researchers needed some fancy equipment - namely, a mass spectrometer.

These devices use an electrical field to separate and identify the components of complex compounds. The instrument they lined up in Boston was originally designed to study the sequence of proteins involved in human disease. But its great sensitivity makes it useful to paleontologists as well.

"Imagine an identity bracelet; each bead on it is a different letter. Then imagine that you randomly break it. By analyzing those fragments, we can figure out how to put it back together and determine what the original sequence of letters was," said John Asara, director of the mass spectrometer core facility at the Beth Israel Deaconess Medical Center in Boston and an author of the study.

Even so, getting enough pure protein from the T. rex femur was tough. "There was a brown gritty material" in the T. rex bone, Asara said. "We were successful in actually purifying enough [protein] to cross the threshold of the mass spectrometer."

Sadly, experts note, the very process of analyzing a bone specimen tends to destroy it, which makes these investigations one-shot operations.

"You need to realize that most curators of dinosaur paleontology don't like me," Schweitzer said. "They want their dinosaur bones intact. They don't like me to come in and dissolve them away."

In the end, they managed to sequence seven collagen protein fragments, containing only 10 percent of the information that it's possible to get from a normal sample.

Still, when they searched a protein database for matches from 20 species, two of the fragments matched perfectly to chicken collagen, giving it the lead in the dinosaur descendant race. But the frog and newt were close behind, with one best match each.

The sequences from the rest of the T. rex fragments were found in the collagen of a variety of animals.

Scientists noted that the database they used wasn't universal, so they couldn't say whether species that weren't in it - such as alligators and different types of birds - might snatch away the chicken's title for most Tyrannosaurus-like.

"Based on what we have, the bird is the winner" said Lewis Cantley, a systems biologist at Harvard Medical School and an author on the mass spectrometry study.

To narrow the field, scientists will need more data. But where can they come up with more prehistoric protein?

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