Scientists may have found the first fossilised dinosaur heart. According to an article in the current issue of the journal Science, the heart appears to have four chambers and provides the best evidence yet that dinosaurs are closely related to birds.
What appears to be a fossilised heart was found inside the chest cavity of what had once been a 300 kg Thescelosaurus. The remains of this creature were found embedded in sandstone in South Dakota in 1993. Scientists believe that the animal, which has been nicknamed Willo, was buried in waterlogged sand immediately after its death, leaving its remains in an oxygen-poor environment that allowed some of the dinosaur's tissues to petrify before decomposition could begin.
"The specimen has a heart," said Dr Dale Russell, a paleontologist at NC State and the leader of the research team. "And by looking at computer-enhanced images of it, it is apparent that it has a single aorta, which suggests that it is more like the heart of a mammal or a bird than the heart of a reptile."
Previously, most dinosaur experts had considered dinosaurs to be cold-blooded animals like reptiles. But the discovery of the fossilised heart suggests that the animals were warm-blooded and had a high metabolic rate. If this is true, they could fight longer and run faster than had been thought.
"This has huge implications for the study of dinosaurs," Dr Russell said. "This challenges some of our most fundamental theories about how and when dinosaurs evolved. It's going to take some getting used to."
In addition to possessing the shape and structures of a heart, the fossilised tissue is also the correct size for a dinosaur heart. According to Dr Reese Barrick, a paleobiologist on the team, an animal that weighs 300 kg should have a heart that weighs between 1.5 and 1.8 kg. Willo's heart weighed between 1.6 and 1.9 kilograms.
But not all of Dr Russell's colleagues agree with the findings. Prof Paul Sereno, at the University of Chicago, has doubts that the NC State team has found a heart.
"We don't have any record of a finding like this in a setting like this," Prof Sereno said. "All of the tissue fossils that have been found have been in things like lake beds and amber, places where there is no oxygen available. And I'm not sure that it resembles a heart - I don't know that you can say that on the basis of the images they have."
But Dr Russell is confident in his findings and is working on reassessing his view of the dinosaur world. He is quick to point out that finding that dinosaurs have larger hearts does not mean that they had larger brains. "Now I see them as very active animals that acted without any foresight," Dr. Russell explained. "Let's face it. The stupidity of the dinosaur world would make us weep."