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RALEIGH, North Carolina -- The first-ever discovery of traces of a dinosaur heart in a fossil has provided evidence that some of the long-extinct beasts were quick -- like warmblooded birds -- rather than slow and plodding -- like some reptiles.
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"This came as a shock because we didn't believe we'd find a heart," said Dale Russell, senior research curator at the North Carolina Museum of Natural Sciences and a paleontologist at North Carolina State University. "No one in his right mind could find a dinosaur heart from 66 million years ago."
The fossil, on display at the museum, was discovered in 1993 in South Dakota and nicknamed "Willo" -- in honor of the wife of a rancher who owns the discovery site. It was exceptionally well-preserved, so the researchers decided to examine it with medical imaging technology at a local hospital.
Computerized tomography -- or CT scan -- images were sent to the university. Researchers then were able to see through the layers of dirt and fossilized bone and discover a 3-D view of the heart with four highly developed chambers and a single arched aorta.
"The single aorta completely separates the oxygen-rich blood from the oxygen-poor blood and sends it to all parts of the body," said Russell, a co-author of the study appearing Friday in the journal Science.
"This challenges some of the most fundamental theories about how and when dinosaurs evolved," he said.
Most reptiles have three-chambered hearts, but even in those with four chambers, such as the crocodile, the blood is pumped through double arteries that mix oxygen-heavy blood with oxygen-lean blood, Russell said.
Coldblooded reptiles are dependent on the environment for body heat. Warmblooded mammals and birds generate their own body heat and are more tolerant of temperature extremes.
Some dinosaur experts said discovery of the fossilized heart will change basic views about the dinosaur and send researchers scrambling to do more X-ray studies of intact specimens.
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"Willo" is a member of the group of dinosaurs known as Tescelosaurus, a 600 pound, hog-like plant eater, about the size of a pony. A long bony tail gave it a total length of about 13 feet.
Russell said the creature probably had to be very fast to survive in a world where giant meat eaters ruled.
"It probably liked to live in brushy terrain, around deadfalls, and could probably go through that terrain just like a torpedo," said Russell.
"This animal lived near the end of the age of reptiles, so it was highly evolved," he said. This suggests that by the end of the dinosaur era, about 65 million years ago, many, if not all, of the dinosaurs had complex hearts and high metabolic rates, Russell said.
"Most people feel that birds evolved from one kind of dinosaur," Russell said. "But our bad luck was to find the other kind of dinosaur, and unfortunately it has a bird-like heart too. So this means that bird-like hearts may be typical of highly evolved, late-in-the-era, dinosaurs -- they were evolving, they were changing."
Researchers theorize that not all dinosaur hearts would be the same.
"I think all the dinosaurs were different, that there was a lot of diversity," said Michael Stoskopf, a clinical ecologist at North Carolina State University. "And we're going to find different systems in different dinosaurs as we look for them."
Now researchers who are skeptical of the link between dinosaurs and birds will have a chance to study the heart, further fueling the debate over the origins and evolution of the dinosaurs.
