Images: ELIZABETH BRAINERD
Presentations given to the Society of Vertebrate Paleontology usually revolve around the remains of long-dead beasts. So it was a change of pace when, at its annual meeting earlier this fall in Bozeman, Mont., University of Massachusetts biologist Elizabeth Brainerd discussed data not from, say, fossil sauropod or theropod dinosaurs but from living reptiles and amphibians. That said, the paleontologists in the audience did not excuse themselves or settle into their seats for a snooze. Rather they listened in rapt attention, because although at least 65 million years separate these modern creatures from Tyrannosaurus rex and its fellow thunder-lizards, they may hold the key to better understanding dinosaur physiology.
In fact, several recent studies have looked to dinosaurs' closest living relatives for insight into aspects of their biology that don't fossilize particularly well, such as how they smelled, breathed and regulated their body temperature. The results are breathing new life into some of the most spectacular animals ever to walk the earth.
For her part, Brainerd looked at creatures ranging from leopard geckos to American alligators, focusing on rhythmic fluttering movements of the throat known as buccal oscillations. These subtle, non-breathing-related movements, she explains, take two forms: the open-mouth variety (also known as gular flutter) and the closed-mouth kind. Each appears to serve a distinct purpose. Gular flutter, seen commonly in heat-stressed lizards, birds and crocodilians, appears to aid in thermoregulation by enhancing evaporation from the respiratory tract. Closed-mouth buccal oscillation, on the other hand, draws air over the tissues lining the nasal passages and may therefore assist in smell. (Mammals, in contrast, use respiratory sniffing.)
The widespread use of buccal oscillation among living reptiles and amphibians, Brainerd observes, suggests that dinosaurs, too, exhibited these behaviors. Thus, during its Cretaceous heyday, T. rex would probably have performed closed-mouth oscillations to sniff out prey¿or gular flutter to cool off after chasing it down.
So far the known dinosaur remains that preserve relevant anatomy fit neatly with this suggestion. In the exquisitely complete fossil of the pint-size predator Scipionyx, for example, remnants of the hyoid¿a structure that in mammals supports the tongue¿are consistent with it having been used to expand and compress the throat for closed-mouth buccal oscillation or gular flutter, Brainerd notes. The shape and position of these features in large dinosaurs¿such as the famed T. rex "Sue"¿and pterosaurs are likewise consistent with this scenario.
Image: ¿Science/Painting by M. W. SKREPNICK, under the direction of L. M. WITMER.
The "Rostral Nostril" Rule
In another presentation made at the same meeting, Lawrence Witmer of Ohio University described a similar investigative approach. Witmer, whose findings also appeared in the August 3 issue of the journal Science, decided to look at modern birds, lizards and crocodilians to get a better idea of where in the dinosaurs' huge bony nostril openings their small fleshy nostrils would have resided. (Whereas the small bony nostril opening in humans doesn't leave much room for debate over the position of the fleshy nostril, the same feature in dinosaurs such as the sauropod Diplodocus can span half the length of the skull.)