Freak Frogs Use Bones as Claws

This weird behavior was observed by biologists from Harvard University in a species of frogs known as Trichobatrachus robustus and is manifested by a break in the bones in the toe pads, forming a new claw-like bone which then penetrates through living tissue, probably as a defense mechanism. David Blackburn from the Harvard University's Museum of Comparative Zoology, who discovered the feature, says that similar behavior has been observed in some salamander species, which push their ribs through the skin, although this is the first time when an actual breaking of bones mechanism is observed.

About nine out of eleven species of the Astylosternus genus living the Cameroon seem to be expressing similar behaviors. "Some other frogs have bony spines that project from their wrist, but in those species it appears that the bones grow through the skin rather than pierce it when needed for defense", says Blackburn.

The claws found in the Trichobatrachus robustus' back feet rest inside the toe tip connective tissue and stick to a piece of bone in the tips through a collagen mass. The opposite side of the claw is tied to a muscle that, when the frog is feeling threatened, contracts and separates the claw from the bone, pushing it downwards to pierce out through the toe pads.

The mechanism is unique in its way, since in other vertebrates the claws are not made of bone only nor do they pierce living tissues to emerge. Only dead specimens have been studied so far, but Blackburn believes that when the frog no longer feels threatened, the muscle seems to relax allowing the claw to slide back inside the toe pad.

"Being amphibians, it would not be surprising if some parts of the wound heal and the tissue is regenerated", Blackburn said.

In areas where such species live, they are hunted and eaten by the local inhabitants. "This is an incredible story. Some frogs grow spines on their thumbs during breeding season, but this is entirely different. For me, it highlights the need for a lot more research on amphibians especially in light of the threat of mass extinctions", says Ian Stephen, curator of herpetology at the Zoological Society of London.