Spine (zoology)

The spines of most spiny mammals are modified hairs, with a spongy center covered in a thick, hard layer of keratin and a sharp, sometimes barbed tip.

An ancient synapsid, Dimetrodon, had extremely long spines on its backbone that were joined together with a web of skin that formed a sail-like structure.

The primary function of these rigid spines are generally presumed to be defensive against predators, but other proposed roles are as cutwaters to reduce drag or as holdfasts against subsurface currents.

The urticating bristles or setae on many caterpillars and New World tarantulas are essentially tiny detachable spines that can cause severe irritation upon contact.

In the case of some large species of stingray, a puncture with the barbed spine and the accompanying venom has occasionally been fatal to humans.

[5] Because many species of fish and invertebrates carry venom within their spines, a rule of thumb is to treat every injury as if it were a snake bite.