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Scales are a defining characteristic of all reptiles. Some have smooth scales, some have rough scales and a small number of reptiles have evolved to develop spikes too. In turn, predators have evolved to see spiked reptiles as a potentially dangerous prey, because of the injury risk that killing and eating them poses. Reptilian spikes are formed from hardened skin or bone and act as both armor and deterrent.
The thorny devil lives in the Australian outback, a flat and exposed habitat where speed on foot is a great asset, both in hunting and avoiding capture. The thorny devil, with his short legs, isn’t blessed with speed, so the foxes, bobcats, coyotes and snakes that hunt him have no trouble catching him. But he has a secret weapon: His back and head are adorned with spikes of varying lengths. His spikes not only make it painful to launch an attack, they also act as a deterrent. If killed, the thorny devil will be a very painful meal to digest.
The bearded dragon is another of the few lizard species that has a spiked back, but these spikes are soft. Like the nonpoisonous animals that have evolved to resemble their poisonous counterparts, the bearded dragon has evolved to appear more dangerous than he actually is to deter predators. His soft spikes would cause minimal pain to a predator, but through this act of evolutionary mimicry, the bearded dragon appears to predators as an animal that could cause injury if attacked.
Similar to the bearded dragon, iguana spikes are for show. You can brush your hand along the spine of an iguana without injury, as the spikes are soft. Despite the lack of physical protection, they act as a useful deterrent to would-be predators. They may also have another function; Martin Christoph Wikelski, professor of ecology at the University of Illinois in Champaign-Urbana, speculates that the spikes are used as a weapon when iguanas fight with each other.
Crocodiles and Alligators
Crocodilian reptiles are blessed with a tough, armor-like outer shell that makes it extremely difficult for other creatures to inflict serious injury on them. A crucial feature of this armor is the osteoderm, a bony plate that forms a spike on the skin. These bony plates protect alligators and crocodiles from injury, which is just as well, because reptilian skin takes a long time to heal if punctured. This means that any reptile with a flesh wound is at great risk of developing potentially fatal skin infections.
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