New studies shed light on facial features of popular dinosaurs

"I almost expect a backlash as a result of our findings. There is a sense that we're changing the way a lot of dinosaurs look," says Lawrence Witmer, an assistant professor of anatomy at Ohio University and principal investigator on a National Science Foundation project to study the soft tissues of dinosaurs.

Witmer presented his research at the annual meeting of the Society for Vertebrate Paleontology held Sept. 30 to Oct. 3 in Snowbird, Utah.

Witmer's project, which has involved high-tech scanning of dinosaur fossils and dissection of their modern-day relatives, has yielded more than just a picture of the internal construction of these animals. The work has led to what Witmer believes may be a better, more accurate way to rebuild dinosaurs using basic comparative anatomy.

"When you work on extinct animals, there is a pressure and a sincere desire to know what these animals looked like," Witmer says. "We draw these pictures and they look right to us because they remind us of animals we see today. But these pictures may be wrong."

For example, Witmer says, Triceratops and Leptoceratops, both ornithischians, have long been thought to have fleshy cheeks, which scientists believed were involved in how these plant-eaters ate. The idea that they had cheeks was based on scientists' comparison of these dinosaurs to modern-day mammals, such as sheep.

The dinosaurs probably were about the same size as sheep -- Leptoceratops is thought to have been about 6 to 8 feet in length, weighing between 100 and 150 pounds -- and most likely enjoyed the same plant-based diet. Sheep, like all mammals, have fleshy, muscular cheeks. Scientists who compared the animals to ornithischians operated under the assumption that these dinosaurs had the same muscular cheeks as sheep.

"Scientists have regarded these cheeks as one of the most important facial features of this group of dinosaurs because of the role muscular cheeks were supposed to play in feeding and perhaps even the efficiency with which they chewed," Witmer said.

Studies of fossil remains of ornithischians suggest these dinosaurs have "features on their jaw bones that require explanation," Witmer says, describing the features as "excavated areas on the upper and lower jaws resulting in the teeth being set in from the surface of the skull." Since the presence of cheeks would explain this jaw structure, scientists' claim that ornithischians had cheeks was strengthened.

But Witmer's studies have found this comparison to be false: modern mammals with muscular cheeks do not have the same sort of excavated area on their lower and upper jaw that is found in dinosaur fossils. A more likely conclusion is that these jaw features supported an extended beak, similar to the beaks on eagles or crocodiles.

It also appears scientists have made a similar mistake with tyrannosaurs, which have been likened to modern-day lizards thought to have muscular lips. Lizards have scales that Witmer says hang down along the edges of their jaws and hide the lizards' teeth when their mouths are closed. However, this isn't necessarily so with tyrannosaurs. These dinosaurs had skin that probably extended to the margin of their jaw but didn't extend to cover their teeth.

"Lips on a tyrannosaur are important if you're making a movie or a toy for a child, but it's really not a big deal if you're trying to figure out what these animals were like," Witmer says. "With or without lips, tyrannosaur was a vicious hunter."

But in a society so mesmerized by dinosaurs, it is important that the experts who recreate these extinct animals in the form of plastic or moveable machines do so accurately, Witmer says.

"People who put cheeks or lips on dinosaurs are trying to put something on these animals that they probably didn't have," Witmer says. "We're not trying to lay waste to other people's ideas without offering alternatives. What we're suggesting is that the way we've made these comparisons in the past is inappropriate and there are better, more disciplined ways to do this that we believe will lead to a more accurate description of how these animals looked."

Since his study began a little more than two years ago, Witmer has examined the fossil remains of dozens of dinosaurs using images obtained by CT scans. His research also has included the dissection and CT scanning of many modern-day animals he says have bone structures and soft tissues similar to dinosaurs.

"Scientists need to get dirty," Witmer says. "They need to roll up their sleeves, pull out their scalpels and start looking at how modern animals are put together. And birds and crocodiles should be the first place we look to make comparisons."

Most scientists agree that birds and crocodiles are the closest living relatives to dinosaurs, which is why it is so puzzling that scientists haven't looked to these animals when recreating physical structures of dinosaurs.

"I think what happens is that we look for an overall match to physical appearance," Witmer says. "When we look at a duck-billed dinosaur, we tend to see an antelope, even though the bone structures of these two animals are different."

Many of these comparisons haven't been scrutinized before because they weren't made using a technique that could be scrutinized, Witmer says. That's one of the differences between methods of old and the one he's developed.

"One of the things I like to take pride in is that this method has the possibility of being proved wrong," Witmer says. "I like to think it can survive testing, but at least it can be tested."

Witmer holds an appointment in the College of Osteopathic Medicine at Ohio University. Other authors of the studies presented at the Utah conference include Michael Papp, a graduate student in geological sciences, and Jayc Sedlmayr, a graduate student in biological sciences, both at Ohio University.