The peculiar pose of many fossilized dinosaurs, with wide-open mouth, head thrown back and recurved tail, likely resulted from the agonized death throes typical of brain damage and asphyxiation, according to two American palaeontologists.
A classic example of the posture, which has puzzled palaeontologists for ages, is the 150 million-year-old Archaeopteryx, the first-known example of a feathered dinosaur and the proposed link between dinosaurs and present-day birds.
According to Kevin Padian, professor of integrative biology and curator in the Museum of Paleontology at the University of California, Berkeley, "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".
Dinosaurs and their relatives, ranging from the flying pterosaurs to Tyrannosaurus rex, as well as many early mammals, have been found exhibiting this posture.
Till now, the explanation usually given by palaeontologists is that the dinosaurs 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.
The two scientists, Padian and Cynthia Marshall Faux of the Museum of the Rockies, however, believe that dinosaurs died in this posture as a result of damage to the central nervous system.
The posture is well known to neurologists as opisthotonus and is due to damage to the brain's cerebellum. In humans and animals, cerebellar damage often results from suffocation, meningitis, tetanus or poisoning, and typically accompanies a long, slow death.
Some animals found in this posture may have suffocated in an ash fall during a volcanic eruption, the researchers said. "This puts a whole new light on the mode of death of these animals, and interpretation of the places they died in. 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," said Prof. Padian.
The findings appear in the March issue of the quarterly journal Paleobiology.