Featured Research

from universities, journals, and other organizations

When Threatened, A Few African Frogs Can Morph Toes Into Claws

Date:
June 25, 2008
Source:
Harvard University
Summary:
Some African frogs carry concealed weapons: when threatened, these species puncture their own skin with sharp bones in their toes, using the bones as claws capable of wounding predators. At least 11 species kick at predators with sharp, protruding bones as a defense mechanism.

Close-up of the foot of a living Trichobatrachus robustus showing the white bony claws protruding from the tips of the toes.
Credit: David C. Blackburn

Biologists at Harvard University have determined that some African frogs carry concealed weapons: When threatened, these species puncture their own skin with sharp bones in their toes, using the bones as claws capable of wounding predators.

The unusual defense mechanism is described by Harvard's David C. Blackburn, James Hanken, and Farish A. Jenkins, Jr., in a forthcoming issue of the journal Biology Letters.

"It's surprising enough to find a frog with claws," says Blackburn, a doctoral student in Harvard's Department of Organismic and Evolutionary Biology. "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."

"Most vertebrates do a much better job of keeping their skeletons inside," he adds.

Blackburn first became aware of the clawed frogs while conducting fieldwork in the central African nation of Cameroon. When he picked up one of the hulking fist-sized frogs, it flailed its hind legs violently, scratching him and drawing blood.

Back in the U.S., Blackburn examined museum specimens of 63 African frog species. He noticed that in 11 species -- all in the genera Astylosternus, Trichobatracus, and Scotobleps and all native to central Africa -- the bones at the ends of the toes were pointed and hooked, with smaller, free-floating bones at their tips. Eventually he determined that these small nodules at the tips of the frogs' feet were connected to the rest of the toe by a collagen-rich sheath.

"These nodules are also closely connected to the surrounding skin by dense networks of collagen," Blackburn says. "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."

This claw-like structure is no conventional claw, though: It is pure bone, free of the keratin sheath that normally surrounds vertebrate claws. And unlike a claw that retracts into a specialized structure in an animal's foot, as in cats, the site where the frogs' foot bones emerge appears to be covered with ordinary skin.

While these frogs were mentioned in the scientific literature on a few occasions from 1900 to 1925, they are generally little-known in the U.S., appearing in few museum collections. Even the handful of researchers who wrote about them a century ago often misinterpreted the piercing of the skin as damage incurred during preservation of specimens.

The frogs are widely roasted and eaten in Cameroon, where hunters -- evidently well aware of the risk of injury -- go to great lengths to avoid handling them when alive.

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

Of more than 5,500 known frog species, Blackburn and his colleagues found just 11 with claws, and speculate there may be another couple of similarly equipped species.

Blackburn plans to study live specimens of the African frogs to determine whether retraction of the foot bones back into the body is an active or a passive process, and how the damaged skin regenerates after the claws are deployed.

"We suspect, since the frog does suffer a fairly traumatic wound, that they probably use these claws infrequently, and only when threatened," Blackburn says.

Blackburn, Hanken, and Jenkins' work was funded by the National Science Foundation's AmphibiaTree project and by a Putnam Expeditionary Grant from Harvard's Museum of Comparative Zoology.


Story Source:

The above story is based on materials provided by Harvard University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Blackburn et al. Concealed weapons: erectile claws in African frogs. Biology Letters, 2008; 1 (-1): -1 DOI: 10.1098/rsbl.2008.0219

Cite This Page:

Harvard University. "When Threatened, A Few African Frogs Can Morph Toes Into Claws." ScienceDaily. ScienceDaily, 25 June 2008. <www.sciencedaily.com/releases/2008/06/080623125003.htm>.
Harvard University. (2008, June 25). When Threatened, A Few African Frogs Can Morph Toes Into Claws. ScienceDaily. Retrieved September 19, 2014 from www.sciencedaily.com/releases/2008/06/080623125003.htm
Harvard University. "When Threatened, A Few African Frogs Can Morph Toes Into Claws." ScienceDaily. www.sciencedaily.com/releases/2008/06/080623125003.htm (accessed September 19, 2014).

Share This



More Plants & Animals News

Friday, September 19, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Elephant Undergoes Surgery in Tbilisi Zoo

Raw: Elephant Undergoes Surgery in Tbilisi Zoo

AP (Sep. 18, 2014) Grand the elephant has successfully undergone surgery to remove a portion of infected tusk at Tbilisi Zoo in Georgia. British veterinary surgeons used an electric drill to extract the infected piece. (Sept. 18) Video provided by AP
Powered by NewsLook.com
Chimp Violence Study Renews Debate On Why They Kill

Chimp Violence Study Renews Debate On Why They Kill

Newsy (Sep. 17, 2014) The study weighs in on a debate over whether chimps are naturally violent or become that way due to human interference in the environment. Video provided by Newsy
Powered by NewsLook.com
Some Tobacco Farmers Thrive Amid Challenges

Some Tobacco Farmers Thrive Amid Challenges

AP (Sep. 16, 2014) The South's tobacco country is surviving, and even thriving in some cases, as demand overseas keeps growers in the fields of one of America's oldest cash crops. (Sept. 16) Video provided by AP
Powered by NewsLook.com
Scientists Given Rare Glimpse of 350-Kilo Colossal Squid

Scientists Given Rare Glimpse of 350-Kilo Colossal Squid

AFP (Sep. 16, 2014) Scientists say a female colossal squid weighing an estimated 350 kilograms (770 lbs) and thought to be only the second intact specimen ever found was carrying eggs when discovered in the Antarctic. Duration: 00:47 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins