Tests Confirm T. Rex Kinship With Birds

In the first analysis of proteins extracted from dinosaur bones, scientists say they have established more firmly than ever that the closest living relatives of the mighty predator Tyrannosaurus rex are modern birds.

The research, being published Friday in the journal Science, yielded the first molecular data confirming the widely held hypothesis of a close dinosaur-bird ancestry, the American scientific team reported. The link was previously suggested by anatomical similarities.

In fact, the scientists said, T. rex shared more of its genetic makeup with ostriches and chickens than with living reptiles, like alligators. On this basis, the research team has redrawn the family tree of major vertebrate groups, assigning the dinosaur a new place in evolutionary relationships.

Similar molecular tests on tissues from the extinct mastodon confirmed its close genetic link to the elephant, as had been suspected from skeletal affinities.

“Our results at the genetic level basically agree with what has been seen in skeletal data,” John M. Asara of Harvard said in a telephone interview. “There is more than a 90 percent probability that the grouping of T. rex with living birds is real.”

Dr. Asara and Lewis C. Cantley, both of Beth Israel Deaconess Medical Center and Harvard Medical School, processed the proteins from tissue recovered deep in bones of a 68 million-year-old T. rex excavated in 2003 by John R. Horner of Montana State University. Mary H. Schweitzer of North Carolina State University discovered the preserved soft tissues in the bones.

For the molecular study, Dr. Asara and Chris L. Organ, a researcher in evolutionary biology at Harvard, compared the dinosaur protein with similar protein from several dozen species of modern birds, reptiles and other animals.

Dr. Organ was the lead author of the journal report, which concluded that the molecular tests confirmed the prediction that extinct dinosaurs “would show a higher degree of similarity with birds than with other extant vertebrates.” The researchers said they planned to extend their investigations to include comparisons of T. rex protein with more species of birds, reptiles and other dinosaurs.

Dinosaur paleontologists were not surprised by the findings. An accumulation of fossil evidence in recent years had given them increasing confidence in their contention that birds descended from certain dinosaurs.