When threatened, frogs can turn their toes into claws

Harvard University biologists have just discovered that some African frogs carry secret weapons: when threatened, frogs use sharp bones in their toes to pierce their skin to Make claws capable of hurting enemies.

The frog's unusual defense mechanism is David C. Blackburn, James Hanken, and Farish A. Jenkins, Jr. of Harvard University described in the upcoming issue of Biology Letters.

Blackburn, a postdoctoral student at Harvard's Department of Evolutionary and Organic Biology, said: 'It's amazing to find frogs with claws. We were even more surprised to see those claws pierce through their skin. These are the first vertebrate animal claws that function in such a way. '

He added: "Most vertebrates often keep their bones inside."

Blackburn first discovered clawed frogs when he conducted research in Cameroon's central African country. When he lifted a clumsy frog the size of a fist, its hind legs jerked violently. He raked him to blood.

Returning to the United States, Blackburn examined the museum's exhibits containing 63 African frog species. He recognized 11 of them, all of them Astylosternus, Trichobatracus, or Scotobleps, and all are endemic to central Africa. They have bone protruding at the tips of the toes, very pointed and arched along with the bones that move freely at the top. Finally, he learned that the small bones in the tip of the toe were attached to the rest of the toe thanks to a covering of collagen.

At least 11 species of frogs can attack enemies with sharp bones emerging as a defensive weapon.(Photo: www.amnh.org)

Blackburn said: ' These small clips are also very tightly attached to the surrounding skin thanks to the dense collagen network. Looks like they work to keep the skin in place relative to claw-like bones. So when the frog flexes a certain muscle on the foot, the sharp bone will leave the tab and pierce through the skin. '

The aforementioned claw-like structure is not the same as a normal claw: it is completely bone, without the keratin shell usually surrounding the vertebrate claws. Normal claws, such as those of cats, shrink into a specialized structure located on the feet of animals. While that specialized part in frogs is only covered by normal skin.

Although these frogs were mentioned in scientific literature around 1900 to 1925, they were very little known in the United States. They also appear only in a few collections at the museum. Even many scientists documenting them for the past century are often mistakenly assuming that the skin that is pierced is a mistake that occurred during the preservation of the specimen.

They are often baked and meat cups in Cameroon, where hunters - who are well aware of their ability to deal damage - try to avoid touching them at all costs when they are alive.

Blackburn said: 'Cameroon hunters often use long spears or machete to avoid touching frogs. Some people even shoot them '.

Of the more than 5,500 known frog species, Blackburn and his colleagues found 11 species with claws. They argue that perhaps in nature other species are equipped with similar weapons.

Blackburn intends to study surviving African frogs to determine the action of withdrawing the leg bones into the body as a proactive or passive process, and how the frog can recover the damaged skin after Use claws.

'We suspect that because the frogs suffer a rather unpleasant wound, they probably use claws infrequently, only when threatened by enemies.'