Nov 8

Despite their thick skins, crocodilians are actually more sensitive to touch than humans, according to new research.

Black caiman portrait

Black caiman with jaws open

Crocodilians – a group comprising crocodiles, alligators and gharials – possess large numbers of dome-shaped dots around their jaws, but until now the function of these structures has been unclear.

Previous theories suggested that the bumps were used to detect electrical or magnetic fields, to secrete fluid or to detect salinity. However, new research published in the Journal of Experimental Biology has found that the unusual structures are extremely sensitive to touch. In fact, they are even more sensitive than human fingertips.

When I used a calibrated series of fibres to touch or tickle the [bumps], I found that they were responsive to forces finer than our own fingertips – a sensory system widely studied for its own sensitivity,” said Duncan Leitch, one of the authors of the study.

Close-up photo of Nile crocodile teeth

Close-up of Nile crocodile jaws, showing black bumps on the skin

Network of nerves

When the researchers analysed the bumps, they found that they were made up of many specialised cell receptors. Numerous free nerve endings occurred near the surface of the bumps, while deeper in the skin were structures sensitive to pressure and vibrations.

By tracing the nerves, the researchers also found that the Nile crocodiles and American alligators they studied had a delicate network of nerves running throughout their jaws, threading through the skull before ending in the bumps. The scientists suggest that this layout, with the nerve network largely enclosed within the skull, may help to protect the nerves during aggressive encounters or when the animal is hunting.

Photo of American alligator walking

American alligator

Sensitive armour

The super-sensitive nature of crocodilians’ jaws may play a role in their rapid reaction times when hunting, allowing them to effortlessly detect movements in the water. It may also allow these armoured reptiles to more easily distinguish between food and inedible debris.

I was very surprised at these results, especially considering how armoured and scaly the crocodiles and alligators appear,” said Leitch. “However, it seems to make sense that an animal that might need to carefully discriminate between inedible objects and food, especially in dark or nocturnal environments, would be well-served by having an exquisite sense of touch.”

Despite their large size and fearsome reputation, female crocodiles can also be incredibly gentle, using their jaws to help their eggs to hatch, and even carrying their offspring in their mouths. Having highly sensitive jaws is an obvious advantage in performing these delicate, controlled movements.

Photo of female American alligator carrying young

Female crocodilians, like this American alligator, take great care of their eggs and young

Evolutionary puzzle

According to Leitch, one of the goals of the research is to gain a better understanding of how the nervous systems of different species – in this case, crocodilians and humans – have evolved to solve similar problems, such as the processing of touch sensations.

As ancient reptiles that have been around for millions of years, crocodilians can play a key role in our understanding of evolutionary processes.

Nile crocodile eye close-up

Close-up of Nile crocodile eye

It is interesting to consider what adaptations, including possibly sensory capabilities, have made them such robust creatures,” said Leitch.

Read more on this story at BBC Nature News – Crocs have super-sensitive jaws.

View photos and videos of crocodilians on ARKive.

Liz Shaw, ARKive Text Author

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