Dinosaur fossils are rare finds. But the 70-million-year-old bones of a Tyrannosauraus rex recovered from Montana are proving to be even more exceptional than the usual dino remains. Researchers report today in the journal Science that they have recovered soft tissue, including blood vessels, from the ancient creature.

Mary Schweitzer of North Carolina State University and her colleagues studied T. rex remains recovered in 2003 from a quarry in the Charles M. Russell Wildlife Preserve that date to roughly 70 million years ago. The specimen, known as MOR 1125 or B-rex, includes a 107-centimeter-long femur bone. Studying the bones in the lab, the team treated part of the femur with a solution designed to dissolve its mineral components. The substance left behind was a stretchy material that showed blood vessels, bone-building cells known as osteocytes and other organic features when observed under a microscope.

The researchers then compared the material to structures found in the bones of ostriches, because living birds are the closest relatives to dinosaurs available for study. They report similarities in both the branching of the blood vessels and the presence of reddish brown dots, which could be nuclei from endothelial cells that line blood vessels. "Our preliminary research shows that antibodies that recognize collagen [the fibrous protein constituent of bone] react to chemical extracts of this fossil bone, " Schweitzer says. "If further studies confirm this, we may have the potential to learn more not only about the dinosaurs themselves, but also about how and why they were preserved in the first place."