In breakthrough, scientists identify dinosaur proteins
By John Noble Wilford Published: April 13, 2007
In a retrieval once thought unattainable, scientists have recovered and identified proteins in a bone of a well-preserved Tyrannosaurus rex that lived, died and was fossilized 68 million years ago.
The scientists say the success, attained with advanced research techniques, opens the door for the first time to exploration of the molecular-level relationships of ancient, extinct animals, instead of just relying on their skeletal remains.
Dinosaur fossil hunters are planning nine expeditions this summer to search wide and deep for more specimens as promising candidates for similar tests. A few large dinosaur bones already in laboratories might be examined for surviving traces of organic matter.
Previously, the earliest identified ancient proteins were from mammoths that died about 300,000 years ago. The oldest confirmed samples of DNA - which is a more direct bearer of information about molecular evolution, but is more degradable - have come from Neanderthals that lived 30,000 to 50,000 years ago. The extraction of DNA would be necessary for studies in dinosaur genetics and for cloning experiments.
Repeated analysis of the T-rex proteins, the researchers said, uncovered new evidence of a link between dinosaurs and birds, a widely held but contentious hypothesis. Three of the seven reconstructed protein sequences were closely related to chickens. (The scientists resisted being drawn into speculation on the likely taste of a T-rex drumstick.) [Che: Oh c'mon though! YOu know they must have!].
Speaking of the doubts she had had going into the work, Mary Higby Schweitzer of North Carolina State University, the leader of one of the teams, said, "We had always assumed that preservation does not extend to the cellular level" in ancient fossils.
Schweitzer described several tests conducted on soft tissues found deep inside the tyrannosaur's femur, or thighbone, excavated in eastern Montana. She reported the surprising tissue discovery two years ago.
Though barely detectable, proteins of collagen 1, the main organic component of bone, were separated and examined. Fragments, or peptides, of the protein were pieced together into strands of the seven sequences. Three of these reacted with antibodies to chicken collagen. Two others appeared possibly related to living creatures: a frog and a newt.
The findings, Schweitzer and her colleagues wrote, "suggested that, under certain conditions, remnant organic constituents may persist across geological time."
The second team, headed by John Asara of the Harvard Medical School and Beth Israel Deaconess Medical Center in Boston, said its independent tests had confirmed the presence of proteins in the tissue.
The researchers subjected samples of the material extracted by Schweitzer to an examination by mass spectroscopy, which breaks material down to its component parts to determine its mass and chemical makeup. The technology is applied in medical research to analyzing the nature of disease-causing agents more precisely.
Asara said the most difficult part of the research had been making sure that all the "brown gritty contaminants" were separated out of the specimen. After several steps in the purification process, the protein fragments were separated from one another, measured for mass and joined in seven separate strings of amino acid.
Lewis Cantley, a Harvard biology professor on the team, said he was satisfied that the findings were "unlikely due to contamination."
In a press release from Harvard, Cantley said, "Basically, this is the breakthrough that says it's possible to get sequences beyond one million years," which had been thought of as the absolute time barrier for the preservation of organic matter in animal remains. In the fossilization process, minerals replace the constituents of bones, turning them to stone.
Similar tests by Asara's team also isolated and pieced together more than 70 protein fragments from a mastodon estimated to be 160,000 to 600,000 years old. The researchers said this provided further evidence of the staying power of ancient protein.
"We can now start to create relationships between extinct and living organisms," Asara said, adding that the T-rex tests supported the idea "that birds are derived from dinosaurs or are closely related."
Mark Norell, a dinosaur expert at the American Museum of Natural History who was not involved in the research, said the importance of the findings was in showing that "biomolecules could be stable over this long period of time." The evidence of a connection between dinosaurs and chickens is less significant, he said, contending that "all the data already confirm the dinosaur-bird relationship."
The huge tyrannosaur thigh was discovered in 2003 by Jack Horner of Montana State University, a longtime dinosaur paleontologist. It was excavated at a depth of 60 feet, or 18 meters, in the Hell Creek Formation, a dinosaur-rich bed of sedimentary rock underlying much of Montana and Wyoming.
Schweitzer, a biologist affiliated with Montana State as well as North Carolina State, cut into the thick bone and recovered the soft tissues, including blood vessels and possibly cells that, she said at the time, "retain some of their original flexibility, elasticity and resilience." This had never been found in a dinosaur before, and prompted the investigations into the nature of the organic matter.
Horner suggested that the size of the bone and the depth of its entombment accounted for the unusual preservation of the tissues. Thick bones, he said, afford interior matter more protection from environmental degradation. Another factor was that this particular dinosaur was buried in a virtually oxygen-free setting very soon after death.
Horner said paleontologists should look for other candidates for soft tissue retrieval among remains of the largest dinosaurs resting under tens of feet of rock. Such excavations, he conceded, will not be easy. But this will be the quest of more than 100 fossil hunters fanning out this summer in the American West and as far away as the Gobi Desert of Mongolia
