WASHINGTON — Protein retrieved from a 68-millon-year-old Tyrannosaurus rex bone closely resembles the main protein in chicken and ostrich bones and is only distantly related to lizards’, strengthening the popular idea that birds, and not reptiles, are the closest living descendants of dinosaurs.
The new work, being published today in the journal Science, builds on a 2007 analysis showing remarkably close similarities between T. rex collagen and collagen from modern-day chickens, but that work did not include comparisons to other living species. Collagen is the primary protein in bones.
“We had made a very loose connection at first,” said John Asara of Harvard Medical School and Beth Israel Deaconess Medical Center, who led both studies. “Now we’re able to make out robust evolutionary relationships and, with very high confidence, basically group the T. rex dinosaur with birds.”
More is at stake than T. rex’s prehistoric pedigree. Asara and his colleagues say their approach has the potential to redraw the evolutionary tree based on molecular data instead of the comparisons of skeletal remains. Bones can be deceiving, because unrelated animals can have similar structures.
Key to the new finding — and the cause of some controversy — is the Asara team’s claim to have retrieved a smidgen of intact collagen from the fossilized thigh bone of a T. rex. Biological materials generally degrade in the environment, and scientists who work with ancient DNA feel lucky when they find a sample that is 100,000 years old. Yet the T. rex protein specimen is more than 100 times older than that.
Mary Schweitzer, a molecular paleontologist at North Carolina State University in Raleigh who oversaw the extraction, said she was confident that it was dinosaur collagen, preserved because of favorable conditions in the Montana soil where the bone was buried.
The results indicate that T. rex, chickens and ostriches are evolutionary siblings, all descended from a single unidentified predecessor.
