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How do lizards drop their tails?

Imagine if you could drop an entire limb and have it grow back later? It’s a nifty evolutionary trick – but how does it work? We asked an expert.

By Dr Mark Hutchinson • Reading Time: < 1

Image credit: Muhammad Mahdi Karim (GFDL)

A LIZARD SEVERS its tail as a self-defence mechanism in order to distract its predator – this is known as autotomy (literally from the Greek ‘self’ and ‘sever’) or self-amputation.

Lizards are born with a line of weakness in their tail, technically called a fracture plane. If a point on the tail is hit or stressed, the muscles along the fracture plane pull away from one another rather than knitting together – this is known as a reflex muscle spasm. The pulling apart of the muscles causes the tail to fall off along the line of weakness.

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Lizard tail autotomy has developed so that when the tail breaks there is no blood loss, and the tail regrows over six months to a year. The tail skeleton is replaced by a rod of cartilage with new muscles growing along it, producing a replacement tail that is usually shorter and less coloured compared with the original.

Lizards aren’t the only animals capable of self-amputation. Over 200 species of invertebrates are capable of using autotomy for self-defence, and it’s even a beahviour known to be used by mammals – at least two species of African spiny mice can release skin upon being captured by a predator, and later regenerate the lost skin (hair follicles, sweat glands, fur, cartilage and all) with little or no scarring.

Dr Mark Hutchinson is a senior researcher at the South Australian Museum.

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