With only bones for clues, scientists continue to puzzle over many details of dinosaur appearances and physiology. Detective work by a paleontologist at Ohio University now indicates that the creatures' fleshy nasal passages were larger than had been thought, which could lead to more-realistic depictions and greater understanding of their respiratory functions.
In the August 3 issue of the journal Science, National Science Foundation (NSF)-supported researcher Lawrence Witmer reveals that nostrils on many dinosaurs were much farther from the eyes and closer to the mouths than previously depicted. By comparing telltale markings on bones from their present-day relatives, he has shown that many dinosaurs had large nasal passages that might have been important for heat exchange and other key physiological processes.
Witmer is an associate professor of biomedical sciences and an anatomist in the university's College of Osteopathic Medicine. X-ray examinations of skulls from more than 65 surviving dinosaur relatives - including crocodiles, birds and lizards - helped him infer the probable location of cartilage, blood vessels and other soft tissues that made up the extinct creatures' nasal cavities.
He discovered that nearly all animals share these traits, which gives weight to his assertion that previous depictions of dinosaur nostrils were inaccurate.
"Our findings were consistent, even in turtles and mammals," Witmer said. "We saw an unusual commonality of how the nasal components relate and are positioned. It turns out that the nostril positioning applies to almost all animals."
As a result, scientists may have to change the conventional view of dinosaur nostrils, which have until now been based on the placement of cranial cavities near the eye sockets. Witmer found the largest nasal passages in horned dinosaurs like Triceratops, duck-billed dinosaurs, and brontosaurs like Diplodocus, the latter of which was 80 to 90 feet long and weighed more than 40 tons.
Other scientists had studied dinosaur noses, Witmer said, but their focus was primarily on olfactory functions. He isn't only interested in how the animals were able to smell; his main goal is understanding overall dinosaur physiology. As his research progressed, Witmer was surprised to learn that no one had previously examined the position of nostrils.
"Learning the biological rules for assembling the bones of extinct animals, like dinosaurs, is notoriously hard," said Jack Hayes, NSF program director for ecological and evolutionary physiology. "But learning the rules for how to place the rest of the animal on those bones may be even harder. Because both the general public and many biologists are keenly interested in dinosaurs, new tools for reconstructing the anatomy and biology of dinosaurs are valuable. What's exciting about Witmer's findings is that they may make it possible to explore the function of dinosaur respiratory systems in more detail."
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