The Evolution of Crocodylian Skin: Crocodile, Alligator and Caiman 'Supersenses'

Crocodylians are some of the most ancient reptiles on our planet. Consisting of crocodiles, gharials, alligators and caimans, this group possesses adaptations that have allowed them to survive for millions of years. Now, scientists have uncovered something new about these creatures; the skin of crocodylians is sensitive to heat, cold, touch and then chemicals in their environment.

Crocodylians are known for their rough skin--tough epidermal scales that consist of keratin and bony plates for added protection. This natural "armor" keeps these animals safe from predators when they're younger and allow them to survive in the wild. The scales on their heads are particularly unusual since they result from cracking of the hardened skin rather than their shape being genetically determined.

In order to get a closer look at crocodilian skin, researchers investigated sensors known as Integumentary Sensory organs (ISOs). These sensors are located within the scales and have fingertip sensitivity. More specifically, the scientists looked at the ISOs within Nile crocodiles and the spectacled caiman to find out exactly what these micro-organs can "see" and how they're formed.

So what did the researchers find? ISOs appear on the head of developing caiman and crocodile embryos before the skin starts to crack and form scales. It also turns out that Nile crocodiles develop ISOs all over their body. These sensors contain mechano-, thermo- and chemo-sensory receptor-channels. This gives them the combined ability to detect touch, temperature and chemical stimuli.

So what does this mean? These crocodylians can detect surface pressure waves, which allow them to quickly find prey even in the dark. In addition, they can use their ability to sense temperature in order to help them maintain their own body temperatures.

"ISO sensors are remarkable because not only are they able to detect many different types of physical and chemical stimuli, but because there is no equivalent in any other vetebrates," said Michel Milinkovitch, the research who led the study, in a news release. "It is this transformation of a diffuse sensory system, such as we have in our own skin, into ISO which has allowed crocodilians to evolve a highly armored yet very sensitive skin."

The findings are published in the journal EvoDevo.