Imagine you are walking alone in parking lot, when suddenly somebody grabs you by the arm and flashes a knife, demanding your money. Do you A) scream for help, B) try to wrestle the knife away, or C) remove your arm from your shoulder and make a break for it? Disarming your assailant may seem preferable to dis-arming yourself, but for a lizard option C is a likely response.
|A lizard tail left behind. Image by Metatron at Wikimedia Commons.|
You likely have heard before that many lizards can break off their tail when trying to make an escape. This ability is called caudal autotomy; autotomy meaning the ability to shed a limb, and caudal simply being a fancy word for tail. Of course, losing a limb is no simple procedure, and lizards possess many specialized features to make caudal autotomy possible.
There are two main kinds of caudal autotomy in lizards: intervertebral and intravertebral. Intervertebral refers to when the tail breaks between vertebrae, and is considered the simpler and more primitive form. Intravertebral, on the other hand, involves some more complex features. The word intravertebral refers to fracture planes found in the middle of each vertebra in the middle of the lizard’s tail. At these fracture planes, the bone can easily snap in half. This snapping of bone is performed by the lizard itself—when its tail is caught, muscles surrounding the bone just above where its tail is held squeeze tight until the bone breaks. After the bone breaks, the rest of the tail follows: the skin stretches and breaks, muscles detach, any remaining tissue divides, and—POP—the tail falls off!
After snapping your arm off to run from an attacker, you would probably just bleed out in your retreat, but lizards have that covered. In their tails, lizards have sphincters (rings of muscle) along their arteries—vessels that normally carry blood to the tail. When the tail is detached, these sphincters tighten to prevent blood from gushing out. Additionally, their veins, which normally bring blood back from the tail, have valves that prevent blood from flowing backwards, similar to the valves in your heart. And while the lizard makes its escape, the dislocated tail jerks and twitches, which distracts the lizard’s assailant. The tail owes its spastic actions to fast, glycolytic muscles, a variety of muscle that can act quickly and with a lot of force, but wears out quickly.
After our reptilian friend has made its daring escape, it has a new problem—it has no tail. A lizard without its tail is at a disadvantage, just as you would be without your arm. Lizards rely on their tails for several functions, including movement, nutrient storage, and social and sexual behaviors. Fortunately, lizards that exercise caudal autotomy can actually re-grow their tails, a process which itself is highly complex. In lieu of a lengthy explanation of another amazing phenomenon, I’ll share this tidbit: to regain lost nutrients and help recover, some lizards have been known to go back and eat their lost tail! So when you tear off your arm to escape a mugger, don’t forget to return to the scene of the crime to self-cannibalize…or maybe just buy some pepper spray beforehand.
Here you can see that the lizard is caught by the tail, pops it off and runs away, and the tail is left twitching.
Bateman, P., & Fleming, P. (2009). To cut a long tail short: a review of lizard caudal autotomy studies carried out over the last 20 years Journal of Zoology, 277 (1), 1-14 DOI: 10.1111/j.1469-7998.2008.00484.x
Clause, A., & Capaldi, E. (2006). Caudal autotomy and regeneration in lizards Journal of Experimental Zoology Part A: Comparative Experimental Biology, 305A (12), 965-973 DOI: 10.1002/jez.a.346
Gilbert, E., Payne, S., & Vickaryous, M. (2013). The Anatomy and Histology of Caudal Autotomy and Regeneration in Lizards Physiological and Biochemical Zoology, 86 (6), 631-644 DOI: 10.1086/673889