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Spiny mice: If they feel threatened, the rodents shed parts of the skin

Photo: Anadolu Agency / Getty Images

From the outside, the tank is invisible. This is probably the reason why it has remained undiscovered for so long: researchers have discovered surprisingly bony structures in spiny mice that are reminiscent of the shell of an armadillo. The bone plates are hidden under the skin in the tail of the animals, reports a team in the journal "iScience".

The discovery is surprising for two reasons. On the one hand, spiny mice have been researched for a long time, but apparently no one has noticed the conspicuous structures in their tails – until now. On the other hand, such bony plates, called osteoderm in technical jargon, are unusual in mammals living today. Until now, they were only known in armadillos.

Accidental discovery in CT

Biologist Edward Stanley of the Florida Museum of Natural History accidentally found what he was looking for when he examined a spiny mouse with a computed tomography (CT) scanner. Such CT scans allow a detailed look into the body. Stanley needed the images for an online database that would collect information on 20,000 vertebrates, the so-called openVertebrate Project.

When Stanley took a closer look at the shot of the mouse's tail, he paused. The biologist did not know the bony plates he saw from rodents, but from lizards or crocodiles. "Although spiny mice are widely known and often used in all sorts of laboratory experiments, no one had noticed that they had such a thing," Stanley told the New York Times.

It is unclear what the plates are used for, but it is possible that the mice use them to shield themselves against enemies. Or the bony structures are supposed to provide additional protection for the tail, like a kind of chain armor.

In the course of evolution, the bony structures have developed several times. They are typical especially for reptiles. They are also known from extinct mammals, such as the giant sloth, which weighed several tons.

Regrowing skin, nerves, muscles

The hidden chain armor is one of several distinctive features of the spiny mice. For research, they are interesting because they show amazing abilities for self-healing. For example, several types of experiments are known to be able to regenerate skin, muscle, nerves and even parts of the spinal cord.

If they sense danger, some spiny mice shed parts of their tail and skin. The sore spots heal quickly without leaving scars. Not only that: after a heart attack, the mice form new blood vessels.

Stanley and his team now want to find out which genes are responsible for the spiny mouse's unusual tail. And whether other mammals may have such an osteoderm. Because no one has really searched for it, says Stanley.