Scientists have uncovered the closest living relative of the mighty Tyrannosaurus rex. For the first time, researchers have managed to sequence proteins from the long-extinct creature, leading them to the discovery that many of the molecules show a remarkable similarity to those of the humble chicken.
The research provides the first molecular evidence for the notion that birds are the modern-day descendants of dinosaurs, as well as overturning the long-held paleontological assumption that delicate organic molecules such as DNA and proteins are completely destroyed during the process of fossilization.
It also hints at the prospect that scientists may one day emulate Jurassic Park by cloning a dinosaur.
Mary Schweitzer, a paleontologist at North Carolina State University and the North Carolina Museum of Natural Sciences, led a team of researchers in analysing the 68 million year-old leg bone of a T-rex, recovered in 2003.
To her surprise, she found that it still contained a matrix of collagen fibers, a protein that gives bone its structure and flexibility. Working with colleagues at Harvard University Medical Center Schweitzer managed to extract and sequence seven different T-rex proteins.
The results were published yesterday in a series of papers in the journal Science.
"The analysis shows that T-rex collagen makeup is almost identical to that of a modern chicken -- this corroborates a huge body of evidence from the fossil record that demonstrates birds are descended from meat-eating dinosaurs," said Angela Milner, the associate keeper of paleontology at the Natural History Museum in London. "So, it is very satisfying that the molecules have provided a positive test for the morphology."
Schweitzer had already sequenced protein from a woolly mammoth in 2002, but that material was from fossils that were merely 300,000 years old.
When the T-rex's proteins had been isolated, Schweitzer's team compared them with the known proteins in living animals.
"Out of seven sequences, we had three that matched chicken uniquely and we had another that matched frogs uniquely and another that also matched newt uniquely and a couple of others that matched multiple organisms that include chickens and newts," said John Asara of the Beth Israel Deaconess Medical Center in Boston, one of the authors of the study.
Asara said the results supported the view that birds evolved from dinosaurs, but added: "If we had more species in the database to compare it to, such as alligator or crocodile, which have not been sequenced yet, we may also find matches to those species. Based on this study, it looks like chickens might be the closest amongst all species that are present in today's genome databases."
Molecular information like this can help to build better evolutionary family trees between extinct and living organisms.
"The fact that identifiable proteins and amino acids can be recovered from at least some fossil vertebrates has opened up an exciting new field of investigation that may tell us more about the patterns and rates of evolution from the past to the present. And we can now do it from molecules as well as bones," Milner said.
However, Milner counselled against indulging in Jurassic Park fantasies just yet.
"The fact that protein sequences from collagen of a T-rex have been recovered does not mean that we will be able to clone dinosaurs, despite what the makers of Jurassic Park suggest. Cloning any organism needs its DNA which carries the instructions to make a copy. DNA is not a protein, it is not a very stable molecule and it has never been recovered from any organism more than 30,000 years old," Milner said.
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