New Data Bolsters Idea of Warmblooded Dinosaurs : Paleontology: The finding is likely to rekindle debate over humans’ ‘invulnerability to extinction.’

USC and North Carolina researchers have found strong new evidence to support the controversial idea that at least some dinosaurs were warmblooded, challenging the popular view that coldblooded modern-day reptiles are models for dinosaur behavior.

The discovery seems likely to heat up the already intense debate over precisely how dinosaurs lived and changed their environment.

“People have always taken comfort from the fact that dinosaurs were dimwitted, slow-moving, coldblooded giants that were replaced by smart, warmblooded mammals,” said William J. Showers of North Carolina State University, a co-author of the work. “If dinosaurs were warmblooded, we must rethink our invulnerability to extinction and global change.”

A growing body of evidence indicates that many dinosaurs--with the exception of huge, plant-eating creatures like the brontosaurus--were fierce predators that ran on two legs and had a high level of activity incompatible with a coldblooded metabolism. But there has been very little direct evidence for this.

USC paleontologist Reese Barrick said Thursday that he has “the first direct (chemical) evidence” that five dinosaur species he studied were warmblooded.

Using a newly developed test to look at modern animals, Barrick and geochemist Showers found that the chemical composition of bones from the legs and the ribs of warmblooded animals were identical, while the comparable bones from coldblooded animals showed distinct chemical differences.

Most of the dinosaurs they have studied, Barrick said, show the same composition pattern as warmblooded animals.

“This is a lot more convincing than some of the studies that have gone on before,” said paleontologist Philip Currie of the Royal Tyrrell Museum of Paleontology in Drumheller, Canada.

Coldblooded animals such as reptiles are completely dependent on their surroundings--sunlight, the air, warm rock surfaces--to elevate their body temperatures to levels sufficient for foraging, hunting and reproduction. An Asian lizard called the Bengal monitor, for example, spends most of its time motionless, either basking in the sun to get warm enough for a brief, frenetic bout of hunting, or hiding in the shade to prevent overheating, according to paleontologist John H. Ostrom of Yale University.

In contrast, warmblooded animals, which generate heat from the digestion of food and from physical activity, enjoy a tremendous range of movement.

Dinosaurs have traditionally been viewed as coldblooded because they were thought to be ancestors of modern reptiles, which are coldblooded. But researchers now believe that at least some dinosaurs were progenitors of birds, which are warmblooded.

Barrick, a graduate student in the laboratory of emeritus paleontologist Alfred G. Fischer at USC, adapted a technique that he and others had previously used to study ancient ocean temperatures. The technique relies on the fact that oxygen exists in nature in two major isotopic forms. The most common form, oxygen-16, accounts for nearly 99.8% of all the oxygen in the environment. A heavier form, oxygen-18, accounts for most of the rest.

Scientists have known that the ratio of oxygen-18 to oxygen-16 in the bones of animals reflects the temperatures at which the bones were formed--that is, the body temperature while the animal was growing. In a warmblooded animal, temperatures should be the same throughout the body. In a coldblooded animal, the limbs and tail should be cooler.

Barrick and Showers are the first to apply this knowledge to the study of dinosaurs. Using a new technique developed by Showers for measuring the ratios, the team studied them in the limb, tail and pelvic bones of modern animals. For warmblooded animals, like cattle and deer, they found that the oxygen ratio was the same in all of the bones, as they had predicted.

But when they studied the bones of a coldblooded Komodo dragon that had died at the San Diego Zoo, the ratios were quite different. They found that the legs of the dragon had less oxygen-18 because they had been formed at an average temperature as much as 16 degrees lower than the bones in the pelvis.

They then looked at comparable bones from dinosaurs, primarily animals that are believed to have been small and active, such as the ceratopsian, a rhinoceros-like dinosaur. In most cases, they found that the results were comparable to those obtained with the modern mammals: The ratios in the limbs and tail were virtually identical to those in pelvic and rib bones.

The one exception was for bones from an adult camarasaurus, a huge, long-necked, long-tailed animal similar to the brontosaurus. In this case, the results suggested that the dinosaur had been warmblooded while young, then became more like a coldblooded animal as it grew older and larger.

Some researchers had suggested just such a possibility. Large dinosaurs are the ones considered most likely to have been coldblooded because their size would have made it nearly impossible to dissipate the heat they generated.

Dinosaur Discoveries

Paleontologists now believe that many dinosaurs, such as the recently discovered Utahraptors shown here attacking a plant-eating sauropod, were vicious predators whose energetic activities are incompatible with a cold-blood metabolism like that of reptiles.

SOURCE: Dinamation Society International