'Fanged Frogs' Discovered on Sulawesi

Boasting "crazy" evolutionary adaptations, a new group of so-called fanged frogs—cousins of this Luzon fanged frog (file picture)—has been discovered on the Indonesian island of Sulawesi, according to biologist Ben Evans. 

During a recent expedition, thirteen new "fanged" species were seen on Sulawesi for the first time, nine of them new to science, according to a new study led by Evans, a biologist at McMaster University in Canada. 

The "fangs" aren't teeth but bony jaw protrusions—some of which aren't visible past the gumline, said Evans, whose study was published in the August issue of the journal The American Naturalist. Scientists have yet to discover the fangs' purpose, but one possibility is that the frogs use the spikes to help capture food in fast-moving water. The frogs with the largest fangs seem to prey on fish or tadpoles.

An as yet unnamed new fanged-frog species on Sulawesi watches over eggs containing tiny tadpoles. When Sulawesi fanged frogs first arrived on the island millions of years ago, each species evolved similar adaptations—such as guarding eggs laid on leaves. 

"We're seeing repeated incidences of the same adaptation [that] evolved independently," Evans said. "People think with evolution you could run the 'experiment' again and get a different result." The fanged frogs' evolution seems to suggest otherwise.

This frog, so far known only as Limnonectes species T, is one of the nine new fanged frogs discovered on Sulawesi. Unlike on the nearby Philippines, where fanged frogs compete for resources with other frogs, Sulawesi's fanged frogs have no competition. As a result, the Sulawesi amphibians have evolved to fill many evolutionary roles, Evans said.

What's surprising about these frogs is they are so closely related but so morphologically variable"—or physically different, Evans said. For instance, Sulawesi's fanged frogs all share a common ancestor that lived just 15 million years ago, yet they've rapidly diversified in a "striking" way, he said.

Another possible explanation for the frogs' fangs (pictured, Limnonectes species T) is that they're for fighting: Males use the spikes in territorial battles over roosting sites or females.

Luckily, the frogs "certainly do not bite you" with their fangs, Evans said—and the protrusions don't have any venom in them.

A fast-moving river is a typical habitat for the large fanged frogs on Sulawesi. The larger frogs tend to have webbed feet and bigger fangs, apparently to assist in moving and hunting in fast water.

The smaller frogs, which spend more time out of water, have toes rather than webbed feet. "You don't want to walk around with flippers on, if you're on land," Evans said.







Source: National Geographic