Crocs have super-sensitive jaws

American alligator Small black dots are sensitive spots on alligator jaws

Related Stories

Thick-skinned crocodilians are actually more sensitive to touch than humans, according to scientists.

US researchers investigated the dome-shaped dots along the jaws of alligators and crocodiles.

They discovered the bumps were made of specialised cells and were more sensitive than human fingertips.

The neuroscientists suggest the sensitive spots play a major part in the aquatic reptiles' impressive reaction times when hunting.

The findings are published in the Journal of Experimental Biology.

Co-author Duncan Leitch from Vanderbilt University, Nashville, US, commented: "The jaws of crocodiles seem to be unique" and can almost be said to perform some of the tactile functions of human hands.

Mr Leitch explained that because crocodilians' forelimbs are too short to grasp anything, they use their jaws in maternal care - gently cracking open eggs and transporting their young inside their mouths.

Good croc, bad croc

Nile crocodile

This behaviour hints that, in addition to their well-known biting force of up to 2,000 psi, the jaws of crocodiles, alligators and other members of the family are capable of very controlled movements.

The jaws of crocodilian species are dotted with black bumps but until now scientists have been unable to explain the purpose of these features.

The bumps have previously been theorised to be electrical or magnetic field receptors, pores for secreting fluid or salinity detectors.

In the lab, Mr Leitch tested how the features reacted to a variety of stimuli. He found no reaction to salinity or electrical fields but touch was a key trigger.

"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 Mr Leitch.

Analysis of the internal structure of the bumps revealed how they worked.

"I found that there were many specialised cell receptor types - many of which are very similar to those found in human skin," said Mr Leitch.

Under a microscope, he found that there were many free nerve-endings near the surface of the bumps. Lower in the skin he found pressure and vibration-sensitive structures.

High speed video at 500 frames per second shows the nocturnal animal's reactions.

"I was very surprised at these results, especially considering how armoured and scaly the crocodiles and alligators appear," he told BBC Nature.

"However, it seems to makes 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."

Evolutionary jigsaw

Mr Leitch traced the nerve structures and found that the Nile crocodiles and American alligators studied had a delicate network of nerves throughout their jaws, which threaded through the skull before ending in the bumps.

He suggested that this layout, with the network largely encased within the skull, may help to protect the nerves during the crocodilians' familiar displays of aggression when hunting or protecting themselves.

"Although crocodilians are certainly not the ancestors to humans, it is interesting to see how different parts of their forebrain may have evolved to process different sensations," Mr Leitch said.

"One goal with a lot of this research is gaining a better understanding of how very different nervous systems have evolved to solve similar problems."

Mr Leitch added that, as so-called "living fossils" that have survived mass extinction events, crocodilians represent a key part of the evolutionary puzzle.

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

Join BBC Nature on Facebook and Twitter @BBCNature.

More on This Story

Related Stories

The BBC is not responsible for the content of external Internet sites

More from nature

  • Cardinal fish and ostracodFish filmed spitting 'fireworks'

    Film crew captures ostracods' spectacular defensive lightshow that makes predatory fish spit them out.

  • Arapaima'Locally extinct'

    A giant fish which used to dominate the Amazon river is now absent in many areas

  • DragonflyRapid reactions

    Dragonfly's super quick reactions recorded in slow motion by BBC film-makers

  • Wingless adult male of the midge Belgica antarcticaExtreme survivor

    Antarctic midge's small genome may be an adaptation to its extreme environment

  • Myotis midastactus specimen (previously identified as Myotis simus)Golden discovery

    A bat from Bolivia is described as a new species by scientists

  • Dinosaurs 'shrank' to become birds

    Huge meat-eating, land-living dinosaurs evolved into birds by constantly shrinking for over 50 million years, new research shows.

  • Would we starve without bees?

    Honey bees are under threat, and as pollination significantly contributes to the food we eat, what would we do without them?

  • Eggshells may act like 'sunblock'

    Birds' eggs show adaptations in pigment concentration and thickness to allow the right amount of sun for embryos, scientists say.

  • Female shrimps are more aggressive

    Female snapping shrimps are more aggressive than males when defending their territories despite their smaller claw size, a study shows.

BBC iWonder

  • Honey bee close-upInsect intelligence

    Are honey bees as smart as your sat nav?

  • Tyrannosaurus rex skull (c) Mark Williamson / Science Photo LibraryDinosaur dynasty

    One group of dinosaurs survived and their descendants can be seen all around us today

  • Brown rat cluse upRise of the rodent

    Reports of giant, 'super rats' are filling the headlines. But why are we being overrun by rats?

  • Cuckoo portraitHoliday hotspot

    What makes the UK such an attractive destination for visiting wildlife?

There have been 75 solar eclipses and 167 major volcanic eruptions in my lifetime

Nicole Malliotakis on Twitter comments on the events that have happened since she was born by using our personalised Your Life on Earth interactive infographic.

Get Inspired


More Nature Activities >

Copyright © 2015 BBC. The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.