African Frogs Can Morph Their Toes into Claws

June 24, 2008

Harvard University biologists this week announced that at least 11 species of African frogs can morph their toes into claws when they feel threatened. To do this, they puncture their own skin with pointy bones in their toes. These sharp bones can then do some serious damage to predators and anyone else that ticks off the frogs.

"It's surprising enough to find a frog with claws," said David Blackburn, one of the scientists. "The fact that those claws work by cutting through the skin of the frogs' feet is even more astonishing. These are the only vertebrate claws known to pierce their way to functionality."

He added, "Most vertebrates do a much better job of keeping their skeletons inside."

(African Clawed Frog)

He and his colleagues made the determination the good old fashioned and painful ways at first. They were conducting field work in Cameroon. After picking up one of the "hulking fist-sized frogs, it flailed its hind legs violently," and wound up scratching him and drawing blood. He survived the frog attack and returned to the U.S., where he analyzed multiple frog museum specimens. They revealed that African frogs in the genera Astylosternus, Trichobatracus, and Scotobleps all possess toes with bony, hooked ends. These are topped by small "free-floating bones."

"These nodules are also closely connected to the surrounding skin by dense networks of collagen," Blackburn explained. "It appears they hold the skin in place relative to these claw-like bones, such that when the frog flexes a certain muscle in the foot, the sharp bone separates from the nodule and bursts through the skin."

Unlike most claws, like the smooth-feeling ones on a cat, these frog weapons are pure bone. Victims smaller than human researchers can then get ripped to smithereens, should the frog choose to deploy its secret weapons.

As an aside, these same frogs are roasted and consumed in Cameroon. It's no wonder that multiple anecdotal reports of scratched hunters exist.

"Cameroonian hunters will use long spears or machetes to avoid touching these frogs," Blackburn says. "Some have even reported shooting the frogs."