Dinosaurs May Have Been Warm-Blooded

By PAUL RECER AP Science Writer WASHINGTON (AP) APRIL 20, 2000 — The remains of a 66 million-year-old dinosaur suggest that the extinct creatures were warmblooded — not coldblooded as once believed — and capable of the swift and sustained motion typical of modern birds and mammals. A modern medical X-ray of a dinosaur fossil named Willo found clear evidence that the animal had four heart chambers that sent blood directly to and from the lungs and then pumped the oxygen-rich blood to the body through a single arched aorta, similar to how the human heart works. "The single aorta completely separates the oxygen-rich blood from the oxygen-poor blood and sends it to all parts of the body,'' said Dale A. Russell, senior research curator at the North Carolina Museum of Natural Sciences and a paleontologist at North Carolina State University "The single aorta is really important,'' 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.'' 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, said Russell. 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. Birds and mammals also have more physical endurance and can be swifter. 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. "It's fantastic. It's way cool,'' Jack Horner, a famed dinosaur researcher at Montana State University in Bozeman, said of the discovery. "It is a landmark in the field.'' Horner said finding the heart in the fossilized remains "strongly suggests that all dinosaurs were warmblooded.'' If verified by other studies that a rock-hard mass in the fossilized chest is a heart, it will mark the first time that scientists have been able to study the cardiac system of dinosaurs. The discovery came in the remains of a member of a group of dinosaurs known as Tescelosaurus, or "marvelous lizard.'' The precise species has not been identified, but researchers have called it "Willo'' in honor of the wife of a rancher who owns the discovery site in South Dakota. Russell said the animal was about the size of a pony and weighed about 660 pounds. A long bony tail gave it a total length of about 13 feet. It had short legs, ate plants and was probably 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. Big animals would have a hard time following so the Willo "probably did quite well,'' he said. "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. Michael Hammer, a co-author of the study, found the nearly intact dinosaur fossil in Harding County, S.D. in 1993. The specimen was recovered without disturbing the dark mass in the chest cavity. It was suspected that the mass could be soft tissue that somehow fossilized with the animal's bones. Usually dinosaur specimens bear no trace of soft tissue, which usually decays before it can become fossilized. Dr. Andrew A. Kuzmitz, an Ashland, Ore., physician and amateur paleontologist, later examined the specimen with a CT scan, a form of medical X-ray that gives details of internal structure. He said seven cardiologists looked at the images and identified the object as a heart with separated pumping chambers similar to the human heart. Paul Fisher, director of an imaging lab at the North Carolina State University veterinarian school, enhanced the CT scan data into three-dimensional images. He said the presence of a four-chambered heart became obvious. "You could see both ventricles (lower heart chambers) and the aorta (a major artery),'' said Fisher, the first author of the study. Fisher said that two veterinarian experts have looked at the images and agreed that the chest mass is the fossil of a four-chambered heart. Developing a four-chambered heart and a high metabolic rate could have been essential to survival for dinosaurs like Willo, which would have been choice morsels for the big meat eaters, such Tyrannosaurs Rex, said Fisher. Coldblooded animals are sluggish in chilly weather and would have been easy prey. Horner said that because of the Willo study by North Carolina scientists, he and other researchers will now start doing CT scans on any intact dinosaur fossils they find. "There are several around like that and I think we'll all start looking at them,'' said Horner. Among the effects of the heart discovery, said Horner, is a boost for the idea that birds evolved from dinosaurs, a theory that is becoming more widely accepted by paleontologists. Birds also have four-chambered hearts.