Casting (tails)

Autotomy (from the Greek auto- "self-" and tome "severing") or self-amputation is the behaviour whereby an animal sheds or discards one or more of its own appendages, usually as a self-defense mechanism to elude a predator's grasp or to distract the predator and thereby allow escape. Some animals have the ability to regenerate the lost body part later.

Some lizards,salamanders and tuatara that are captured by the tail will shed part of the tail structure and thus be able to flee. The detached tail will continue to wriggle, creating a deceptive sense of continued struggle and distracting the predator's attention from the fleeing prey animal. Depending upon the species, the animal may be able to partially regenerate its tail, typically over a period of weeks. The new section will contain cartilage rather than regenerating vertebrae of bone, and the skin of the regenerated organ generally differs distinctly in colour and texture from its original appearance. The technical term for this ability to drop the tail is caudal autotomy. In most lizards that sacrifice the tail in this manner, breakage occurs only when the tail is grasped with sufficient force, but some animals, such as some species of geckos, can perform true autotomy, throwing off the tail when sufficiently stressed, such as when attacked by ants.

Caudal autotomy in lizards takes two forms. In the first form, called intervertebral autotomy, the tail breaks between the vertebrae. The second form of caudal autotomy is intravertebral autotomy, in which there are zones of weakness, fracture planes across each vertebra in the mid-part of the tail. In this second type of autotomy the lizard contracts a muscle to fracture a vertebra, rather than break the tail between two vertebrae.Sphincter muscles in the tail then contract around the caudal artery to minimize bleeding. Caudal autotomy is prevalent among lizards; it had been recorded in 13 of approximately 20 families.

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Wikipedia