London, May 28 : Biologists have described a bizarre, hairy frog, which in a gruesome process, actively breaks its own bones to produce cat-like extendable claws.
According to a report in New Scientist, the frog, known as Trichobatrachus robustus, has been described by David Blackburn and colleagues at Harvard University's Museum of Comparative Zoology.
The researchers believe that the gruesome behaviour of this frog is a defence mechanism, also observed in nine of the 11 frogs belonging to the Astylosternus genus, most of which live in Cameroon.
T. robustus actively breaks its own bones to produce claws that puncture their way out of the frog's toe pads, probably when it is threatened. This indicates that this gruesome behaviour might serve as a defence mechanism for the frog.
The claws of T. robustus, found on the hind feet only, are nestled inside a mass of connective tissue. A chunk of collagen forms a bond between the claw's sharp point and a small piece of bone at the tip of the frog's toe.
The other end of the claw is connected to a muscle.
Blackburn and his colleagues believe that when the animal is attacked, it contracts this muscle, which pulls the claw downwards. The sharp point then breaks away from the bony tip and cuts through the toe pad, emerging on the underside.
The end result may look like a cat's claw, but the breaking and cutting mechanism is very different and unique among vertebrates. Also unique is the fact that the claw is just bone and does not have an outer coating of keratin like other claws do.
Because Blackburn has only studied dead specimens, he said that he's unaware what happens when the claw retracts - or even how it retracts.
It does not appear to have a muscle to pull it back inside, so the team thinks it may passively slide back into the toe pad when its muscle relaxes.
"Being amphibians, it would not be surprising if some parts of the wound heal and the tissue is regenerated," said Blackburn.
"Some frogs grow spines on their thumbs during breeding season, but this is entirely different," said Ian Stephen, curator of herpetology at the Zoological Society of London, UK. "For me, it highlights the need for a lot more research on amphibians especially in light of the threat of mass extinctions," he added.