For the first time, researchers have sequenced proteins from the long-extinct Tyrannosaurus rex, the mightiest of dinosaurs, 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 theory that birds are the modern-day descendants of dinosaurs and overturns the long-held palaeontological assumption that delicate organic molecules such as DNA and proteins are destroyed during fossilisation. It also hints at the tantalising prospect that scientists may one day be able to emulate Jurassic Park by cloning a dinosaur.
Mary Schweitzer, a palaeontologist at North Carolina State University, led a team of researchers in analysing the 68-million-year-old leg bone of a T-rex recovered in 2003 in Montana. To her surprise, she found it still contained a matrix of collagen fibres, a protein that gives bone its structure and flexibility.
Working with colleagues at Harvard University Medical Centre, and with equipment normally used to identify and sequence tiny amounts of protein in human cancers, Schweitzer managed to extract and sequence seven different T-rex proteins.
The results were published last week in a series of papers in the journal, Science.
”The analysis shows T-rex collagen make-up 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 palaeontology at London’s Natural History Museum.
Schweitzer sequenced protein from a woolly mammoth in 2002, but that material was from fossils merely 300 000 years old.
When the T-rex’s proteins had been isolated from the surrounding dust and rock, Schweitzer’s team compared them with the known proteins in living animals.
”Out of seven sequences, we had three that matched chicken uniquely, another that matched frogs uniquely, another that 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 Centre in Boston, one of the study’s authors.
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 might also find matches to those species. Based on this study, it looks like chickens might be the closest of all species 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 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,” said Milner.
Jack Horner of Montana State University said sequencing the T-rex protein would also lead to a new era in palaeontology, which has so far relied on looking at the shapes and sizes of fossil bones to infer the relationships between extinct animals. The important thing was to find well-preserved material that had been protected from water and air.
Lewis Cantley, a biologist at Harvard University who helped analyse the T-rex proteins, said the techniques used had pushed medical technology to its limits. ”The exciting thing is that this technology is still in its infancy, we’re going to see it get a lot better.”
However, Milner counselled against indulging in Jurassic Park fantasies just yet. ”Cloning any organism needs its DNA, which 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.” — Â