Previously, scientists had visualized fleshy nostrils placed at the back of the bony opening, perhaps, Witmer remarks, because early on, scholars posited that the big sauropods spent most of their time in the water. In that case, an upward-facing nostril positioned nearly atop the creature's head could have served as a sort of snorkel. Since then, however, researchers have revised their ideas about sauropod ecology, now favoring a largely terrestrial existence for these beasts. Yet the idea of a dorsal nostril persisted¿and became the standard for all sorts of dinosaurs.
Witmer's work may put that notion to rest. His observations show that the relationship between flesh and bone in 45 species representing the dinosaurs' closest living kin clearly follows a "rostral nostril" rule. That is, the fleshy nostril occupies a spot in the front of the bony opening, not the back. From an engineering standpoint, this position makes for a much better nose. Rostral nostrils would have allowed air to travel the length of the nose through the complex conditioning, humidifying and filtering systems commonly seen in large dinosaurs. A dorsal nostril, in contrast, would have let the air bypass this apparatus, Witmer notes. (Fleshy nostrils placed near the mouth may have also enhanced the animal's ability to smell.)
The Alligator and the Treadmill
Though we do it without thinking, breathing is a complex activity involving multiple components. Still, scientists thought they had it largely figured out for a number of animals. But the results of a third study shows that they may yet have a lot to learn. Monitoring the breathing of alligators walking on treadmills, University of Utah biologists Colleen Farmer and David Carrier discovered a previously unknown role of the pelvis in alligator respiration. The findings suggest that dinosaurs may have employed the same odd mechanism to help them breathe.
Image: SALLY BENSUSEN/Visual Science Studio
Most reptiles cannot breathe deeply while on the move because the same muscles that control the ribs during breathing also help the trunk bend from side to side when walking. Alligators, however, can perform both activities simultaneously because they don't rely exclusively on the rib muscles to breathe. When an alligator inhales, a muscle called the diaphragmaticus (comparable to our own diaphragm) pulls the liver back toward the tail. Because the liver is attached to the lungs, this backward motion helps expand the animal's chest and lungs. Then, during exhalation, the liver slams forward into the lungs, forcing the air out.
Scientists have known about the alligator's unusual liver-pump system for some time. But Farmer and Carrier found more to the story. Gator hips¿unlike those of mammals, including humans¿are moveable. As it turns out, certain muscles pull the front of the pelvis down when the animal inhales, expanding the abdominal cavity. This leaves more room for the liver and the muscles that pull it backward. Blood can thus flow freely from the alligator's tail back to its heart, giving the beast more endurance.
Ironically, this enhanced endurance is largely wasted on the gator, which takes a rather passive approach to prey capture, lurking quietly until some unfortunate creature wanders across its path. Dinosaurs, on the other hand, may have made good use of it: Farmer and Carrier note that birds also possess a moveable pelvis that assists in breathing. The close relationship of birds and alligators to dinosaurs, they say, suggests that dinosaurs, too, used their hips to breathe.