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 Fossil studies have long suggested modern birds were descended from T. rex, based in similarities in their skeletons.
Now, bits of protein obtained from connective tissues in a T. rex fossil shows a relationship to birds including chickens and ostriches, according to a report in Friday's edition of the journal Science.
"These results match predictions made from skeletal anatomy, providing the first molecular evidence for the evolutionary relationships of a non-avian dinosaur," Chris Organ, a postdoctoral researcher in biology at Harvard University said in a statement.
Co-author John M. Asara of Harvard reported last year that his team had been able to extract collagen from a T. rex and that it most closely resembled the collagen of chickens.
They weren't able to recover dinosaur DNA, the genetic instructions for life, but DNA codes for the proteins they did study.
While the researchers were able to obtain just a few proteins from T. rex, they have now been able to show the relationships with birds.
With more data, Organ said, they would probably be able to place T. rex on the evolutionary tree between alligators and chickens and ostriches.
"We also show that it groups better with birds than modern reptiles, such as alligators and green anole lizards," Asara added.
The dinosaur protein was obtained a fossil found in 2003 by John Horner of the Museum of the Rockies in a barren fossil-rich stretch of land that spans Wyoming and Montana. Mary H. Schweitzer of North Carolina State University and the North Carolina Museum of Natural Sciences discovered soft-tissue preservation in the T. rex bone in 2005.
The research of Organ and Asara indicates that the protein from the fossilized tissue is authentic, rather than contamination from a living species.
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 The researchers also studied material recovered from a mastodon fossil and determined it was related to modern elephants.
Their research was funded by the National Institutes of Health, National Science Foundation, Paul F. Glenn Foundation and the David and Lucille Packard Foundation.
Meanwhile, in another paper in Science, researchers report refining a method to determine ancient dates that will allow them to better pinpoint events such as dinosaurs' extinction.
A team led by Paul Renne, director of the Berkeley Geochronology Center and an adjunct professor of earth and planetary science at the University of California, Berkeley, said they were able to refine the so-called argon-argon dating method to reduce uncertainty. The method compares the ratio or two types of the element argon found in rocks.
The greater precision matters little for recent events in the last few million years, according to Renne, but it can be a major problem for events in the early solar system. For example, a one percent difference at 4.5 billion years is almost 50 million years.
The new system reduces that potential uncertainty to one-fourth of one percent, the researchers said.
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[Associated
Press; By RANDOLPH E. SCHMID]
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