What is the mechanism that lets animals drop limbs?

How exactly do crabs and lizards drop limbs/tails? How are they able to make a part of their body just fall off on command? If the limb can come off so easily, wouldn’t it be prone to breaking off by accident? Could you easily yank a lizard’s tail off, or does the lizard have to do the ‘detaching’ for it to come off easily?


As an analogy, if an orangutan grabbed some of your hair and tried to carry you up a tree, the hair would likely come out and you’d fall to the ground and scamper away. The orangutan would be left wondering, ‘how did that critter eject its hair like that?’


no, what I mean is these animals can remove their limbs as a defense mechanism. But I’m curious how they are biologically built in such a way that a limb can just come off so easily, muscles, bones, tendons, blood vessels and all.

I only remember this vaguely:
Lizards who can drop their tails have specialized structures that allow the joint to come apart and keep the critter from bleeding to death. They’re called Fracture Planes. They can be arranged in sequence down the tail. This website on legless lizards has some more info in the middle paragraph. Here’s some more info. Apparently the tail grows in on a cartalidge rod!

Not all lizards can drop their tails, though, or at least not easily. My 3 foot long iguana has a tail that’s about 3.5 inches thick at the base. It makes a good handle. If she were to lose her tail there, I’d have to take her to a doctor to make sure she didn’t bleed to death and the tail would never grow back the same, if at all. It might be easier at the thinner points of her tail and it was probably easier when she was young and little.

I’ll bow out to the other herp-minded dopers until I can get home to my books :smiley:

How Lizards Lose Their Tails.