The study, reported in the Aug. 3 issue of the journal Science, will give many dinosaurs a new look: Nostrils once drawn on the top of some dinosaurs' heads now appear just above the mouth. And while that new face likely will capture wide public interest, for scientists, the impact is more than skin deep, said Ohio University paleontologist and study author Lawrence Witmer.
"The public has always been interested in dinosaurs because they're so huge. Scientists have been interested because dinosaurs really seem to stretch the bounds of physiological form," said Witmer, an associate professor of biomedical sciences and anatomist in the university's College of Osteopathic Medicine. "By looking at the noses of dinosaurs and their modern-day relatives, we've potentially been able to provide some answers to how these animals could have survived being so large."
The latest findings from his efforts to reconstruct soft tissues in dinosaurs, a study dubbed the "DinoNose Project"and funded by the National Science Foundation, place dinosaur nostrils a significant physiological distance from where scientists once thought the openings lay.
That misconception dates to the earliest recovered dinosaur fossils, many of which belonged to sauropods. The enormity of these long-necked brontosaurs – some weighing as much as 70 to 80 tons – was matched only by whales, so early paleontologists assumed sauropods also must have been aquatic animals. Nostrils high on the forehead would have allowed the dinosaurs to breathe while partially submerged. The assumptions were reinforced with the 1884 discovery of an intact skull of the sauropod Diplodocus, which revealed a large hole at the top of the head that scientists believed held the entire nasal cavity.
"Despite the fact that many years later we realized sauropods weren't primarily aquatic, we never addressed the nostril position again," Witmer said. "And somehow, we translated that nostril position to other dinosaurs."
But Witmer's studies suggest the nasal region of dinosaurs is much larger than previously thought, and the hole paleontologists once said was a nostril actually was just one part of the nasal cavity. The fleshy nostrils, he discovered, actually lay farther forward and closer to the mouth. And not just in the sauropods, where the change is visually evident, but in all dinosaurs.
"The change in nostril position is indeed most striking for sauropods, but it also will make a big difference for horned and duck-billed dinosaurs," Witmer said. "Biologically it'll make a huge difference for all kinds of dinosaurs."
Witmer's research suggests that many of the large dinosaurs he's studied – Diplodocus was 80 to 90 feet long and weighed more than 40 tons – had highly vascular nasal cavities that took up more than half of some of the animals' skulls. Such a complicated nasal structure would be involved in a host of biological functions: Conditioning, humidifying and filtering air on its way to the lungs, the exchange of gases and regulating brain and body temperature.
The position of the nostrils is key to the organization of the entire respiratory system. If the nostrils of dinosaurs were in the back, as paleontologists once believed, this complicated nasal system couldn't have participated in many of the animal's basic biological functions.
Having nostrils down front offers many other evolutionary advantages as well, Witmer added. Smell is very important for animals that must rely on scent to find a mate, detect a predator and find food. And close proximity between two such strong collectors of sensory information – the nostrils and the mouth – makes sense from a physiological standpoint. But this wasn't the evidence that convinced Witmer that dinosaurs' nostrils had been positioned incorrectly.
Because the fossil record only preserves bone, paleontologists look to dinosaurs' modern-day relatives to reconstruct soft tissues such as muscles, veins and arteries. So for this project, Witmer studied 62 animals from 45 species of crocodiles, birds and lizards, documenting the placement of soft tissues through dissection and hundreds of X-rays. Soft tissues etch markings on bone, leaving behind a specific signature. By comparing these bony signatures of modern-day animals to similar markings on fossils from dozens of dinosaurs, Witmer was able to map the likely position of cartilage, blood vessels and other soft tissues that made up the nasal cavity of dinosaurs.
"We looked at as many modern-day animals as we could get a hold of," Witmer said, "and found an extraordinary amount of evidence to suggest the nostrils of dinosaurs actually were parked out front."
What's more, the common "up-front" placement of fleshy nostrils in the reptiles, birds and mammals Witmer studied suggests an unusual anatomical trait consistent among these animals. This adds yet another evolutionary twist to Witmer's research, which is offering as much insight into modern-day animals as it is for animals that have been extinct for millions of years.
The next phase of Witmer's work includes studies of the nasal cavity's possible role in regulating brain and body temperature. And although his analysis of data collected during the DinoNose Project will continue for years to come, he now is expanding his research to include studies of dinosaurs' jaws and limbs, work that could once again alter scientists' and society's perceptions of how dinosaurs looked.
While changing the appearance of dinosaurs may not be among Witmer's research goals, it has been an undeniable result of the work he's done. Earlier studies by Witmer presented at past Society for Vertebrate Paleontology annual meetings stripped the lips from Tyrannosaurus rex and the cheeks from Triceratops.
"People like to think of dinosaurs as looking a certain way, and often times, they're given traits that are more familiar, more comfortable," he said. "As a scientist, I'm certainly not out to change dinosaurs' appearance. But what our studies are doing is allowing the true uniqueness of the animals to emerge."
Written by Kelli Whitlock.
Contact: Lawrence Witmer, 740-593-9489; witmer@exchange.oucom.ohiou.edu
Journal
Science