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Planet Earth

Spiky-Skulled Frogs Head-Butt Enemies to Deliver Deadly Toxins

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Aparasphenodon brunoi (Bruno's Casque-headed Frog). (Credit: Carlos Jared/Butantan Institute) Two species of highly toxic frogs have a bone to prick with their predators. Corythomantis greeningi and Aparasphenodon brunois frogs, native to Brazil, have skin secretions that are more deadly than the venom of pit vipers. A single gram of A. brunois secretions could kill 80 humans. But unlike poisonous amphibians, these frogs have an additional trick up their sleeve: They have spikes growing on their skulls, and when danger is near, they head-butt predators to ensure the toxic payload hits its mark.

Not Your Typical Poisonous Frog

Of course, there are hosts of brightly colored frogs with toxin-producing skin glands. For most species, simply producing toxins is enough to keep predators at bay, or at least get the final word if eaten. However, C. greeningi and A. brunois aren’t your typical poisonous frogs. In fact, they aren’t poisonous at all; they’re venomous.

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A head close-up showing the lip of a Corythomantis greeningi (Greening's frog). (Credit: Carlos Jared/Butantan Institute) For an animal to be considered venomous, the creature needs to have two things: poison, and a mechanism to deliver said poison. Snakes have fangs, for example. Scientists have known about C. greeningi and A. brunois for decades, but they didn’t know much about their anatomy or behavior. Well, one day while gathering specimens in the field, that all changed for Brodie and Carlos Jared of Instituto Butantan in São Paulo. In a study, published Thursday in Cell Press, they wrote:

“One of us (C.J.) was injured on the hand by the spines of C. greening while collecting frogs, causing intense pain radiating up the arm, lasting about 5 hours.”

Carlos was on the wrong end of a toxic head-butt.

Spikes of Doom

The incident captured Brodie and Carlos’ attention, and so they took a closer look at both A. greeningi and A. brunois in the lab. They found that both species use skull spines to pierce their own epidermis to expose spike in areas of the skin packed with poison glands – kind of like retractable claws. For these frogs, the poison glands are concentrated near the nose and lips. So when the frogs are restrained, they release a thick secretion, flex their heads and jab their faces into the skin of their captor.

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This is the spiky skull of Corythomantis greeningi, (Greening's frog). (Credit: Carlos Jared/Butantan Institute) Everyone knows about poisonous frogs, but researchers say it was a surprise to find two species of truly venomous frogs. The finding has piqued researchers’ curiosity, and they plan to study several other poisonous frog species that they suspect are actually venomous. But one thing's clear about these critters: When they find themselves in trouble, they know how to use their heads.

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