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The largest carnivore that ever walked the planet - Tyrannosaurus rex - is more closely related to the modern chicken than it is to living reptiles such as the alligator or crocodile, a study of the dinosaur's fossilised protein has found.
Researchers analysed a tiny shred of 68-million-year-old protein taken from the leg of T. Rex and compared it to the same protein found in 21 modern species. They confirmed that the giant predator is closely related to chickens and ostriches, but less closely to reptiles such as alligators and crocodiles, thought to be more closely related to dinosaurs than other living creatures.
It is the first time that scientists have been able to trace a relationship between dinosaurs and birds through molecular analysis of animal protein, although anatomical studies have already produced convincing evidence of a link between birds and dinosaurs.
"These results match predictions made from skeletal anatomy, providing the first molecular evidence for the evolutionary relationships of a non-avian dinosaur," said Dr Chris Organ, an evolutionary biologist at Harvard University in the United States.
Proteins are composed of amino acids arranged in a sequence that mirrors the order of chemical bases on molecules of DNA, so scientists can look at short strands of protein called peptides - to investigate the relationships between species, alive or dead.
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