US:PROTEIN RETRIEVED from a 68-million-year-old Tyrannosaurus rex bone closely resembles the main protein in chicken and ostrich bones and is only distantly related to lizards, strengthening the popular idea that birds, not reptiles, are the closest living descendants of dinosaurs.
The work builds on a 2007 analysis showing remarkably close similarities between T rex collagen and collagen from chickens, but that work did not include comparisons to other living species. Collagen is the primary protein in bones.
"We made a very loose connection at first," said John Asara, of Harvard Medical School and Beth Israel Deaconess Medical Centre, who led both studies. "Now we're able to make out robust evolutionary relationships and, with very high confidence, basically group the T rex dinosaur with birds."
More is at stake than T rex's prehistoric pedigree. Dr Asara and his colleagues say that their novel approach has the potential to redraw the evolutionary tree based on molecular data instead of the traditional comparisons of skeletal remains. Bones can be deceiving, because unrelated animals can have similar structures.
Crucial to the new finding - and the cause of some controversy - is the team's claim to have retrieved a smidgen of intact collagen from the fossilised thigh bone of a T rex.
Biological materials generally degrade in the environment and scientists who work with ancient DNA feel lucky when they find a sample that is 100,000 years old.
Yet the T rex protein specimen is more than 100 times older than that, leading some to wonder whether it might be a more recent contaminant.
Mary Schweitzer, a molecular palaeontologist at North Carolina State University, who oversaw the extraction of the protein, said she was confident they were dealing with dinosaur collagen, preserved because of favourable conditions in the Montana soil where the bone was found.
But Pavel Pevzner, director of the Centre for Algorithmic and Systems Biology at the University of California, San Diego, said his own research, soon to be published, refuted Dr Asara's study, which appeared in yesterday's issue of the journal Science. The findings are "a joke", he wrote in an e-mail. "Serious evolutionary biologists will laugh reading this piece."
It was unclear whether Dr Pevzner disputed the link between birds and dinosaurs or simply distrusted the team's methods.
But Dr Asara said he was so sure of the results he could almost taste them. "Based on this data, you can be very confident that T rex would taste more like chicken than it did last year."