An article in this week's issue of the journal Science throws more kindling on the heated debate over whether birds are the descendants of dinosaurs. Researchers say molecular analysis of a shred of 68-million-year-old Tyrannosaurus rex protein — along with that of 21 modern species — shows that dinosaurs share common ancestry with chickens, Ostriches, and to a lesser extent, alligators.
“These results match predictions made from skeletal anatomy, providing the first molecular evidence for the evolutionary relationships of a non-avian dinosaur,” says co-author Chris Organ, a postdoctoral researcher in organismic and evolutionary biology at Harvard.
He and his colleagues published a phylogenetic tree that places Tyrannosaurus in the Archosauria next to Struthio (Ostrich) and Gallus (chickens, or Red Junglefowl).
The research began after John Horner, curator of paleontology at Montana State's Museum of the Rockies, uncovered a T. rex femur bone (left) in 2003 in a barren fossil-rich stretch of land that spans Wyoming and Montana. Two years later, Mary H. Schweitzer of North Carolina State and the North Carolina Museum of Natural Sciences discovered soft-tissue preservation in the bone.
Then John Asara of Beth Israel Deaconess Medical Center and Harvard Medical School, an expert in mass spectrometry techniques, was able to extract precious slivers of collagen protein. (Salvaging DNA from the bone appears to be impossible.)
“We determined that T. rex, in fact, grouped with birds — Ostrich and chicken — better than any other organism that we studied,” he says.
If that wasn't enough, the scientists also report a similar analysis of 160,000- to 600,000-year-old collagen protein sequences derived from mastodon bone. The results establish a close evolutionary relationship between the extinct species and modern elephants. — M.M.