Dinosaur protein sequenced
Lucky find shows up record-breaking fossil.
Palaeontologists have sequenced some protein from a 68-million-year-old fossilized Tyrannosaurus rex bone.
The protein — a key component of bone and connective tissue called collagen — blasts the record for the oldest protein ever sequenced. Before this, the oldest sequenced protein (also collagen) came from a mammoth fossil that was 100,000-300,000 years old. So the new find, reported this week in the journal Science1, is quite a surprise.
Scientists hope that if similar molecular data can be recovered from other fossils, the information can be used to firm up the dinosaur family tree and to better understand their relationship with living animals.
But evolutionary biologists caution that the information from a single type of protein, such as collagen, is inadequate for building a proper family tree.
Nor is sequencing a single type of protein going to open the doors to Jurassic Park. Scientists would need DNA — which is much more fragile — in order to get the full genome of an ancient animal.
"I think it's a really great experiment," says Mark Norell of the American Museum of Natural History in New York. "But is this going to change the way we look at dinosaurs? Well, probably not."
Hard core protection
This particular fossil, which has been shown to contain soft tissues before (see 'Flexible fossil shows tyrannosaur's softer side'), was unusually well preserved.
It was found within 1,000 cubic metres of sandstone in the badlands of eastern Montana. The rock is thought to have kept away damaging groundwater and bacteria. "As the tissues begin to liquefy, the enzymes of decay and degradation are drained away in the sand, whereas in the mud it just sits and stews in its own juices," says Jack Horner, a palaeontologist at the Museum of the Rockies at Montana State University in Bozeman and an author on the study.
Collagen is very abundant and collagen fibres form a particularly tough, triple helix, with three strands of protein wound together like rope. The collagen samples that Schweitzer isolated from the T. rex fossil were buried deep within the fossil's large, dense bones, which probably provided a protective casing for the protein.
Horner is optimistic that similarly well-preserved fossils and their resident proteins can be isolated if palaeontologists are willing to dig through enough rock to find them. "If we spend a lot of time getting as deep into the sediment as we can in places where there has been very little air or water contamination, I think we're going to find that many specimens are like this," he says.
But others question whether there will be enough such finds to be useful. "I think you're not going to be able to get this kind of material from the vast majority of fossils," says Norell. "Most of the stuff we work on has been heated to hundreds and hundreds of degrees and smashed by geological pressure."
"If we can only get rare sequence data it will remain just a curiosity," says Derek Briggs, a curator at Yale University's Peabody Museum of Natural History in New Haven, Connecticut.
Close to a chicken
So far, seven fragments of protein sequence have been gleaned from the T. rex fossil. Trawling through the limited amount of data available on collagen sequences, the authors determined that these are closest to the collagen of chickens2.
This is in keeping with the dominant view that birds and dinosaurs are closely related. But the researchers hasten to point out that this does not mean that T. rex's closest modern relative is the chicken — just that the chicken is the closest relative for which collagen sequence is available in public databases. Crocodile and alligator collagen sequences, for example, were not available for comparison.
Schweitzer hopes the results will also encourage palaeontologists to open their collections to molecular investigation — even though that will mean dissolving the samples to get at any proteins inside. "Most curators of dinosaur palaeontology don't like me," says Schweitzer. "They like to keep their bones intact."
- Schweitzer M. H., et al. Science, 316 . 277 - 280 (2007).
- Asara J. M., et al. Science, 316 . 280 - 285 (2007).