A new study of ancient proteins retrieved from a Tyranosaurus rex fossil confirms the long-hypothesized evolutionary connection between dinosaurs and modern birds, experts say.
The finding is the first molecular evidence that birds, not lizards or other reptiles, are the closest living relatives of dinosaurs, the researchers note.
A close relationship between the two groups was already widely suspected, based on similarities in skeletal features.
The new research follows a breakthrough study last year in which scientists reported the recovery and partial molecular sequencing of T. rex and mastodon proteins.
Both dinosaur studies examined samples of collagen, the main protein component of bone.
In addition to cementing the dino-bird connection, the new study provides the first molecular evidence that mastodons and elephants are also closely related.
"This shows that if we can sequence even tiny pieces of fossil protein, we can establish evolutionary relationships," said co-author John Asara of Harvard Medical School, who also led the previous T. rex study.
Chris Organ of Harvard University is the lead author of the new report, which appears in tomorrow's issue of the journal Science.
From T. Rex to Chicken
The T. rex proteins were extracted from soft tissues preserved inside 68-million-year-old fossil remains first described in 2005.
The mastodon remains were much younger, dating to between 160,000 and 600,000 years ago.
Using a variety of techniques, the researchers compared the T. rex and mastodon protein sequences with those of 21 living animals, including ostriches, chickens, and alligators.
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