Tyrannosaurus rex, meet the chicken 鈥� your third cousin more than 100 million years removed. A new family tree based on protein sequences recovered from dinosaur fossils firms up the dinosaur鈥檚 avian lineage.
鈥淧alaeontologists have known this overall connection. We have now confirmed it with molecular data,鈥� says , a biochemist at Beth Israel Deaconess Medical Center in Boston, who led the study.
His team compared sequences of a collagen protein recovered from a 68 million-year old T. rex fossil and a half-million year old mastodon (a kind of extinct elephant) with those same sequences from 21 modern animals 鈥� including chicken, alligator, elephant and human.
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Family tree
The collagen analysed was collected from a T. rex bone found in Montana. 鈥淲hat makes it possible is that it鈥檚 exceptionally well preserved,鈥� says Asara. 鈥淵ou can鈥檛 walk into a museum and take a bone off a T. rex and get sequence data.鈥�
Asara鈥檚 team had previously sequenced the collagen protein using a technique called mass spectrometry (see our report on the development, Tyrannosaurus rex fossil gives up precious protein).
To build the family tree, Asara and colleague Chris Organ compared the T. rex sequence with collagen from other animals. Those with similar collagen sequences were grouped closely together on the tree, while differences in the sequences suggested the animals had long diverged.
For the most part, the collagen tree captured relationships palaeontologists and evolutionary biologists had little reason to doubt, including T. rex鈥榮 kinship to birds and the mastodon鈥檚 ancestry to elephants.
There was one glaring mistake, however. Asara鈥檚 results suggested the Anolis lizard, a native of the Southeastern US, shared more relations with mammals than with alligators and dinosaurs. Such errors are common when working with limited sequences, Asara says.
Trusty old bones
But Mark Norrell, a verterbrate palaeontologist at the American Museum of Natural History in New York, says such obvious errors question the usefulness of molecular trees, when compared to the old-fashioned kind made by studying bones.
鈥淚t doesn鈥檛 add much new,鈥� he says. 鈥淢ammoths and elephants 鈥� I mean, five-year olds know that.鈥�
, a palaeontologist at the University of Maryland in College Park agrees. 鈥淚 could do a hell of a lot better with bones,鈥� he says.
He says, however, that further study of the T. rex collagen and other samples could help scientists understand the evolution of dinosaurs. 鈥淚 think it鈥檚 cool to see that there is a signal that鈥檚 preserved.鈥�
Holtz may soon get his wish. , a palaeontologist at North Carolina State University in Raleigh, who helped discover the Montana T. rex fossil says: 鈥淲e鈥檙e not done with this dinosaur.鈥�
Journal reference: (DOI: 10.1126/science.1154284)
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