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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.......Mary Schweitzer of North Carolina State University is a co-author of the new study and made the initial discovery of the T. rex soft tissue remains.She has argued that such remains may be relatively common in well-preserved fossils but are often overlooked.Others have said that protein preservation over tens of millions of years should not be possible. Some scientists have continued to question whether Asara's and Schweitzer's sequences really came from an ancient T. rex.Proteins from some other biological source could have somehow contaminated the dinosaur remains, the skeptics note.The new finding that the proteins are most similar to those of birds, Asara said, helps rule out the possibility of contamination from other sources such as mammals.