Crocodiles’ Sensitive Faces Help Understand Ancestors
April 5, 2013

Crocodiles’ Super-Sensitive Face Offers Insight Into Evolutionary History

Watch the video "Measuring a Crocodile's Smile"

redOrbit Staff & Wire Reports - Your Universe Online

The ultra-sensitive nerves in the faces of crocodilians could help biologists understand how both modern and ancient animals interact with their environment, according to a new study in this month´s edition of The Anatomical Record.

These nerves are so sensitive that they can detect changes in a pond when a single droplet of water hits the surface several feet away. Alligators, crocodiles and other members of this reptilian order use these so-called “invisible whiskers” to detect prey while hunting, explained researchers from the University of Missouri (MU).

“The trigeminal nerve is the nerve responsible for detection of sensations of the face,” Casey Holliday, assistant professor of anatomy in the MU School of Medicine, said Thursday in a statement. “While we've known about these sensitive nerves in crocodiles, we've never measured the size of the nerve bundle, or ganglion, in their skulls, until now. When compared to humans, this trigeminal nerve in crocodiles is huge.”

Holliday explains that the trigeminal nerve mechanism known as “face-touch” is basically a way for a creature to communicate with its environment. The animals receive stimuli from the environment that tell them about danger, food and other important information.

Now, Holliday and co-author Ian George, a doctoral student at the MU, are looking at the trigeminal nerve to help determine how its function has evolved over the years. They hope to eventually be able to measure this fiber in other contemporary and historical species in order to learn more about animal behavior.

To do so they will have to focus on a specific hole in the skull. The trigeminal nerve is rooted inside the head of crocodilians, but it must travel through a large hole before it branches out and reaches the skin on the creature´s face. Holliday and George plan to examine the relationships between the sizes of the skull, brain and ganglion in the hopes that they can use that data to learn exactly how sensitive the face is.

“Currently, we rely on alligators, crocodiles and birds to provide us with information about how ancient reptiles, such as pre-historic crocodiles and dinosaurs, functioned. However, the first thing we have to do is to understand how the living animals function,” Holliday explained.

When comparing the size of the trigeminal nerve hole of alligators with those of certain dinosaurs, George said that the hole in the far-larger dinosaur skull is similar in size to — or perhaps even smaller than — those of its modern-day cousins. That knowledge could give scientists more information about how well or poorly dinosaurs could detect small sensation on the face, which in turn could allow them to trace the evolution of this biological mechanism.

“Some species of ancient crocodiles lived on land and they probably wouldn't have a use for a sensitive face that can detect disturbances in the water,” he explained. “So our next step is to trace back and determine when the nerve got bigger and see how that might have paralleled the animals' ecology.”