PROTEIN that resembles chicken has been extracted from a 68-million-year-old Tyrannosaurus rex bone.

The collagen tissue was removed from a fossilised thigh bone belonging to one of the giant predator dinosaurs.

Scientific analysis showed it was structurally similar to chicken protein, providing further evidence of the evolutionary link between dinosaurs and birds.

The bone was unearthed in 2003 in Montana, US. Two years later the find hit the headlines with the discovery that it seemed to contain soft tissues, including blood vessels.

Writing today in the journal Science , the same scientists confirmed they had found fragments of collagen preserved within the fossil.

Collagen is a fibrous, elastic protein that helps to keep skin looking young. It also makes up most of the organic material in bone, which consists of both minerals and protein.

When minerals are removed from human bone, a collagen matrix is left behind.

The US scientists at North Carolina State University in Raleigh performed the same operation on the T.rex fossil, and found what appeared to be residual collagen.

This was a big surprise, since according to current theories of fossilisation it should not be possible for original organic material to survive so long.

Minerals

Fossilisation occurs over millions of years when organic remains are replaced by minerals from water and rock.

Dr Mary Schweitzer, who led the North Carolina team, said: "For centuries it was believed that the process of fossilisation destroyed any original material, consequently no-one looked carefully at really old bones."

The T.rex tissue tested positively against antibodies that are known to react with collagen, but doubts remained.

Final confirmation came from the laboratory of Dr John Asra, director of a mass spectrometry facility at Beth Israel Deaconess Medical Centre in Boston.

Mass spectrometry is a sensitive technique that identifies chemicals by their atomic mass. It was able to show the T.rex material contained sequences of amino acids - protein building blocks - typical of collagen.

The sequence pattern looked like that of chicken collagen, and there were also similarities with frog and newt protein.

"The similarity to chicken is definitely what we would expect given the relationship between modern birds and dinosaurs," said Dr Schweitzer.

"From a palaeo standpoint, sequence data really is the nail in the coffin that confirms the preservation of these tissues.

"This data will help us learn more about dinosaurs' evolutionary relationships, about how preservation happens, and about how molecules degrade over time, which could also have some important medical implications for treating disease."