Two species of Brazilian hylid frog have been identified as the world's first-known venomous frogs. These creatures deliver a powerful toxin through tiny spears affixed to their heads. This poison is powerful enough that a single gram of the substance could kill 80 human beings. 

Aparesphenondon brunoi and Corythomantis greeningi were first discovered decades ago, in the rainforests of Brazil. However, biologists did not know of the spines in the animals until a researcher recently became the victim of an attack from one of the amphibians. 

Carlos Jared of the Butantan Institute in Brazil, was studying a member of a type of hylid frog known as a Corythomantis greeningi, when the animal suddenly bared teeth from behind its upper lip, biting into the upper lip of the researcher. Jared quickly dropped the sharp-toothed frog, and for five hours, pain shot through his arm. 

The term "venomous" is not to be confused with the word "poisonous." Other frogs are known to release toxins, notably the poison dart frog, which releases toxins through its skin, poisoning any would-be attacker. These two species are the first known to inject poison directly into their targets. 

The toxin of C. greeningi is twice as deadly as that of the highly-dangerous pit viper. Later, as investigators continued to explore the Goytacazes National Forest, they came across another venomous frog species — Aparasphenodon brunoi. The toxin of this creature was found to be 25 times as deadly as the toxin of a pit viper. When they ran across this creature, researchers were careful to wear protective gear when handling the animal. 

"Both frogs deliver their venom from head spines resting in toxic glands in their skin. When the animals attack, the skin contracts and the poison-coated spines protrude from the frog's lip. Researchers imagine as a hungry predator closes its mouth over the frog, it begins shaking its head and jabbing the spines into every corner a frog's face can fit," Angus Chen wrote for Science Magazine. 

The two species of venomous frogs identified in this study are not closely related. This suggests to the researchers that other varieties of frogs may have also developed the ability to deliver venom. 

"Discovering a truly venomous frog is nothing any of us expected, and finding frogs with skin secretions more venomous than those of the deadly pit vipers of the genus Bothrops was astounding," Edmund Brodie, Jr. of Utah State University said.

Discovery of the two novel venomous frogs was detailed in the Journal of Herpetology.  

Photo: William Wan | Flickr

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