COLUMBIA — If the 30-foot-long body wasn't enough to intimidate its enemies, the thick-skinned shield on the top of its 5-foot-long head was likely to get the job done. About 95 million years ago, this reptile roamed the Mesozoic Era rivers of Africa and is believed to be the earliest ancestor of modern crocodiles.
Aegisuchus witmeri, or "Shieldcroc" as it has been nicknamed, was discovered by MU researcher Casey Holliday, an assistant professor of anatomy in the MU School of Medicine. The research, published Tuesday in the journal PLoS-ONE (Public Library of Science), was co-authored with Nick Gardner, an assistant undergraduate researcher at Marshall University in *West Virginia, according to a news release from the MU News Bureau.
MU researcher Casey Holliday talks about Shieldcroc in this video from the MU News Bureau.
Holliday's discovery of Shieldcroc makes a good storyline. One day, while working at the Royal Ontario Museum in Toronto, he pulled open a drawer and found "some scrappy looking chunks of skull" that had no identification tags.
"The skull was originally dug up in Morocco by locals, as a part of a fossil trade in Morocco," he explained in his office Tuesday, the reddish chunk of skull in front of him on the desk. "The local people go in and look for things that people will pay for, and a lot of it ends up at gem and mineral shows and rock shops." Museum curators go to those shows and shops and look for things that might be valuable to researchers, he said.
By studying the grooves on the skull that were made by blood vessels, Holliday concluded that the crocodile had a shield-like structure on top of its head that it used to show off and attract other crocodiles. This is similar to the manner in which modern crocodiles lurk in muddy waters with the back of their heads tilted up above the water line, just enough to reveal their ear-like horns and the size of their head.
Another theory is that the shield may have served as a thermo-regulator that helped control the temperature of Shieldcroc's head.
Before Holliday's discovery, such a shield has never been seen on a crocodile.
"It's only a chunk of the skull, but we can actually tell a lot about an animal based on structures associated with the braincase," Holliday said. "We were able to take some measurements from the skull roof and to use CAT scanning to pull out the size and shape of the brain, and use those estimates to see how big the head and the body might have been."
Shieldcroc is also the first close ancestor of modern crocodilians found in Africa. The identification of the species and its unusual head feature can help scientists discover more about the evolution of crocodiles as well as offer new information about how to protect modern reptilian habitats.
Shieldcroc lived in the river systems in Morocco, and river systems typically have a high diversity of animals and are quick to show the impacts of humans, pollution and other changes.
"Understanding the climate of the past, and knowing what we know about climate changes today, it does give us an idea that this type of an ecosystem is a hotbed of diversity, and they are highly susceptible to changes, whether due to the climate, the chemistry of water or carbon dioxide in the air," Holliday said.
Whit Gibbons, professor emeritus of ecology at the University of Georgia, has spent years researching relationships between populations and their environmental conditions.
"Any time scientists acquire information about a species and the relationships with its habitat, we gain insight into how animal communities respond to various components of their environment," Gibbons said.
He said one aspect of studying a prehistoric species is that it provides insight into how a species interacted with its environment without human influences. He said they are "research opportunities that do not exist for present-day species anywhere in the world."
"Such information is applicable to present-day situations in that by understanding how we arrived where we are today in regard to species and habitat relationships, we may be able to have more predictability about future circumstances," Gibbons said.
Holliday plans to give the skull chunk back to the Royal Ontario Museum, where it will be put on display later this year, the MU news release said.
He will continue to research the evolution of crocodiles.
"Researchers are finding a lot of fossils of crocodiles that were terrestrial predatory crocodiles or terrestrial herbivorous crocodiles with adaptations on the teeth to eat plants, as well as all sorts of aquatic crocodiles and fully marine ones," Holliday said. "These prehistoric fossils tell us that today's crocodiles are actually kind of boring."