Measurement of crocodilian nerves to help better understand dinosaur behaviour

Crocodilians have nerves on their faces that are so sensitive, they can detect a change in a pond when a single drop hits the water surface several feet away. Alligators and crocodiles use these "invisible whiskers" to detect prey when hunting. Now, a new study from the University of Missouri has measured the nerves responsible for this function, which will help biologists understand how today's animals, as well as dinosaurs and crocodiles that lived millions of years ago, interact with the environment around them.

Crocodilians’ skin on their faces is incredibly sensitive. A University of Missouri study is examining the size of those nerves to determine how this function has evolved over time [Credit: University of Missouri]

"The trigeminal nerve is the nerve responsible for detection of sensations of the face," said Casey Holliday, assistant professor of anatomy in the MU School of Medicine. "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."

The key to this measurement is a specific hole in the skull. The trigeminal nerve is rooted inside the skull, but must travel through a large hole before it branches out to reach the crocodile's skin on its face. By examining how the skull size, brain size and ganglion size relate to each other, scientists can estimate how sensitive the face is. Eventually, Holliday hopes to measure this nerve in other ancient and contemporary species to learn more about animal behavior.

Crocodilian facial nerves are much more sensitive than humans. This allows the crocodile to detect minute disruptions in water as they hunt for prey or search for a mate [Credit: University of Missouri]

"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," said Holliday, who co-authored the study with doctoral student Ian George. "However, the first thing we have to do is to understand how the living animals function."

When comparing the size of the hole for the trigeminal nerve found in alligators to that of certain dinosaurs, George says that the hole in the much-larger dinosaur skull is very similar in size or even smaller, which could give scientists more information about how well dinosaurs could detect small sensations on the face. From there, the scientists can start to trace the evolution of this nerve and the mechanism used by crocodiles.