T. REX TISSUE OFFERS EVOLUTION INSIGHTS / Scientists discover wealth of genetic clues in amino acids

** EMBARGOED UNTIL 2:00 P.M. EDT, THURSDAY, APRIL 12, 2007 ** Undated handout photo provided by the journal Science showing a T.Rex femur bone. (AP Photo/Science) EMBARGOED UNTIL 2:00 P.M. EDT, THURSDAY, APRIL 12, 2007 / PHOTO PROVIDED BY THE JOURNAL SCIENCE less ** EMBARGOED UNTIL 2:00 P.M. EDT, THURSDAY, APRIL 12, 2007 ** Undated handout photo provided by the journal Science showing a T.Rex femur bone. (AP Photo/Science) EMBARGOED UNTIL 2:00 P.M. EDT, THURSDAY, APRIL ... more Photo: Ho Photo: Ho Image 1 of / 1 Caption Close T. REX TISSUE OFFERS EVOLUTION INSIGHTS / Scientists discover wealth of genetic clues in amino acids 1 / 1 Back to Gallery

When dinosaur hunters discovered the huge thighbone of a teenage Tyrannosaurus rex buried under tons of rock on a Montana cliffside four years ago, they were amazed to find what seemed to be soft tissues still preserved inside the bone after 68 million years.

Few scientists believed that any organic material in a fossil could last that long without turning to stone, but when Mary Schweitzer, a paleontologist at North Carolina State University, removed all the minerals that had formed the bone, she found fragments of tough, ropy fibers and what appeared to be clusters of intact cells and flexible blood vessels.

Under her scanning electron microscope, the material looked identical to blood vessels in modern ostrich bones.

It was the first time anyone had detected soft tissue in a dinosaur fossil, and Schweitzer's tests convinced her that the ropy material was collagen, the main protein of connective tissue that makes bones strong and flexible in all animals, ancient or modern.

Now, with the most sophisticated equipment yet developed to analyze protein tissue, Harvard University researchers have determined the precise sequence of amino acids in seven fragments of Schweitzer's dinosaur collagen -- the first time any tissue from such an ancient fossil has ever been precisely analyzed, and a possible clue to the nature of the genes behind the sequences.

The new tools used by Schweitzer and her Harvard colleagues are yielding novel molecular insights into the evolutionary paths that have led from the dinosaurs to their modern descendants -- the birds of today.

More than that, Schweitzer said Thursday in a teleconference with reporters, the Harvard technology should also help clarify the relationships between long-extinct fossils of many animals whose modern counterparts remain unknown.

Two reports on this first sequencing of amino acids in a dinosaur fossil are being published today in the journal Science. Besides Schweitzer, the authors include John Asara and Lewis Cantley of Harvard Medical School and its Beth Israel Deaconess Medical Center, and John Horner, the famed dinosaur hunter at Montana State University's Museum of the Rockies in Bozeman, Mont.

Horner, who led the fossil excavation, said the dinosaur must have become fossilized in sandstone rather than in wet mudstone after it died near a stream in what was once a sandy wasteland.

Those circumstances help explain how the animal's soft tissues could have been preserved so long.

"If you think about a giant Tyrannosaurus drumstick rotting in the sand," Schweitzer said, "the difference between sand and mud is that as tissues begin to liquefy and suppurate, the enzymes of decay and degeneration are drained away in sandstone, whereas in a mudstone it just sits and stews in its own juices."

Horner said a major expedition this summer will seek more dinosaur fossils in a similar state of "exquisite preservation" embedded in the ancient sandstones of Montana and Mongolia.

The Harvard scientists employed uniquely sensitive new mass spectrometry instruments used for medical research to analyze seven fragments of Schweitzer's dinosaur collagen, weighing a total of only 40 milligrams -- about a thousandth of an ounce.

They found three amino acid sequences that precisely matched those of modern chickens. One matched a newt sequence, one matched a frog, and two matched collagen from chickens and several other animals, Asari said.

Schweitzer said she had also conducted antibody tests of the dinosaur and chicken collagen and found a surprising match there, too.

Besides the dinosaur samples, Asari said he had also been able to sequence protein fragments from a mastodon fossil estimated to be 16,000 to 600,000 years old -- another indication that under the right conditions proteins can remain remarkably stable over longer periods than anyone had previously thought.

In the records of past fossil discoveries, Schweitzer said, soft tissue has never been recovered from anything older than a million years, and she and her Harvard colleagues now hope to sequence the proteins in the cells and blood vessels she found in her T. rex bone.

UC Berkeley dinosaur evolution expert Kevin Padian, who was not involved in this new research, noted that for 15 years molecular biologists had been insisting that Schweitzer could not possibly get molecules out of a 68 million-year-old fossil, and that her methods were flawed despite all the many tests she used that confirmed her work.

"But the lesson, she's saying now, is that nature doesn't work like a lab bench," Padian said. "Chemicals that might degrade in a laboratory over a short period need not do so in a protected natural chemical environment. Mary Schweitzer is just the best there is, so it's time to readjust our thinking."

As for the Harvard work sequencing the ancient protein for the first time, Padian called it "a brilliant technical achievement, and it's because we know that birds evolved from dinosaurs that it makes sense."