T. rex thigh reveals chicken family ties
CHICAGO (Reuters) - Tiny bits of protein extracted from a 68-million-year-old dinosaur bone have given scientists the first genetic proof that the mighty Tyrannosaurus rex is a distant cousin to the modern chicken.
"It's the first molecular evidence of this link between birds and dinosaurs," said John Asara, a Harvard Medical School researcher, whose results were published in Friday's edition of the journal Science.
Scientists have long suspected that birds evolved from dinosaurs based on a study of dinosaur bones, but until recently, no soft tissue had survived to confirm the link.
That all changed in 2005 when Mary Higby Schweitzer of North Carolina State University reported finding soft tissue, including blood vessels and cells, in a T. rex bone dug out of sandstone from the fossil-rich Hell Creek Formation in Montana.
Schweitzer, in another study appearing in this week's issue of Science, found that extracts of T. rex bone reacted with antibodies to chicken collagen, further suggesting the presence of birdlike protein in dinosaur bones.
For his study, Asara used a highly sensitive technology called mass spectrometry to determine the chemical makeup of bone fragments provided by Schweitzer and her team.
He first had to purify the bone extract, which came in the form of a gritty brown powder that remained after minerals were extracted. Asara then broke it down into peptide fragments, little bits of proteins, isolated into the amino acid sequences that make them up.
"It was very tough to get anything," he said in a telephone interview. He wound up with seven separate strands of amino acid, five of which were a particular class of collagen, a fibrous protein found in bone.
Next, Asara had to interpret the sequences. He compared his results to collagen data from living animals. Most matched collagen from chickens, while others matched a newt and frog.
BIRDS OF A FEATHER
"Based on all of the genomic information we have available today, it appears these sequences are closer to birds or chickens than anything else," Asara said.
Ultimately, scientists had hoped to find genetic material that was unique to the T. rex. That was not possible with the tiny T. rex sample.
"We never found unique T. rex tags," he said.
In a similar study of mastodon bones supplied by Schweitzer, Asara had more luck.
He compared the samples to a database of existing amino acid sequences and against a theoretical set of mastodon sequences and found a total of 78 peptides, including four unique sequences.
Still, Asara said the T. rex protein sequence was useful in providing clues about the evolution of the species.
The researchers said the results may change the way that people think about fossil preservation.
"The fact that we are getting proteins is very exciting," said paleontologist Jack Horner, who dug up the T. rex in 2003 and is co-author of the paper with Schweitzer.
Horner said paleontologists will need to dig deeper for specimens that have not been corrupted by ground water and bacteria.
"I think we are going to find that many specimens are like it. It will be a matter of paleontologists getting into sites that are not necessarily easy," he told reporters in a telephone briefing.
