Paleontologists often find dinosaur fossils with heads thrown back, gaping mouths and tails curved toward the head and assumed they died in water and the currents drifted the bones into that position, or that rigor mortis or drying muscles, tendons and ligaments contorted the limbs.

An example of the posture is the 150-million-year-old Archaeopteryx, the first-known specimen of a feathered dinosaur and the proposed link between dinosaurs and present-day birds.

"I'm reading this in the literature and thinking, 'This doesn't make any sense to me as a veterinarian,'" said Cynthia Marshall Faux, a veterinarian-turned-paleontologist at the Museum of the Rockies.

Faux (pronounced "fox") and a colleague say brain damage and asphyxiation are the more likely culprits.

"Virtually all articulated specimens of Archaeopteryx are in this posture, exhibiting a classic pose of head thrown back, jaws open, back and tail reflexed backward and limbs contracted," said Kevin Padian, professor of integrative biology and curator in the Museum of Paleontology at the University of California, Berkeley. He and Faux published their findings last week in the journal Paleobiology.

Some animals found in this death-throes posture may have suffocated in ash during a volcanic eruption, consistent with the fact many fossils are found in ash deposits, Faux and Padian explained. But many other possibilities exist, including disease, brain trauma, severe bleeding, thiamine deficiency or poisoning.

"This puts a whole new light on the mode of death of these animals, and interpretation of the places they died in," Padian said. "This explanation gives us clues to interpreting a great many fossil horizons we didn't understand before and tells us something dinosaurs experienced while dying, not after dying."

The posture appears to be a good indicator the animal was warm blooded, as other research has suggested, because the posture has been seen only in dinosaurs, pterosaurs and mammals, which are known or suspected to have had high metabolic rates. Animals with lower metabolic rates, such as crocodiles and lizards, use less oxygen and so might have been less traumatically affected by hypoxia during death throes, Padian said.