In the 25 March issue of Science, a team led by Mary Schweitzer of North Carolina State University in Raleigh describes finding flexible and elastic blood vessels, and possibly intact cells, in the 68 million-year-old skeleton of a Tyrannosaurus rex.

A stretch? Dissolved T. rex bone yielded flexible, branching vessels (left), some of which contain cell-like structures (right). CREDIT: M. H. Schweitzer

The skeleton was excavated in 2003 from the Hell Creek Formation of Montana by co-author Jack Horner's crew from the Museum of the Rockies in Bozeman, Montana. Back in the lab, Schweitzer and her technician demineralized the fragments by soaking them in a weak acid. As the fossil dissolved, transparent vessels were left behind. "It was totally shocking," Schweitzer says. Branching vessels also appeared in fragments from a hadrosaur and another Tyrannosaurus skeleton. Many of the vessels contain red and brown structures that resemble cells. And inside these are smaller objects similar in size to the nuclei of the blood cells in modern birds.

If the cells consist of original material, paleontologists might be able to extract new information about dinosaurs. For instance, they could use the same sort of protein antibody testing that helps biologists determine the evolutionary relationships of living organisms. "There's a reasonable chance that there may be intact proteins," says David Martill of the University of Portsmouth in the United Kingdom. Perhaps, he says, even DNA might be extracted.

Hendrik Poinar of McMaster University in Hamilton, Ontario, cautions that looks can deceive: Nucleated protozoan cells have been found in 225-million-year-old amber, but geochemical tests revealed that the nuclei had been replaced with resin compounds. Even the resilience of the vessels may be deceptive. Flexible fossils of colonial marine organisms called graptolites have been recovered from 440-million-year-old rocks, but the original material--likely collagen--had not survived.

Schweitzer is seeking funding for sophisticated tests that would use techniques such as mass spectroscopy and high performance liquid chromatography to check for dino tissue. As for DNA, which is less abundant and more fragile than proteins, Poinar says it's theoretically possible that some may have survived, if conditions stayed just right (preferably dry and subzero) for all 68 million years. "Wouldn't it be cool?" he muses, but adds "the likelihood is probably next to none."