Scientists have found that the Indonesian fanged frog is the only known frog species that does not lay eggs, but instead gives birth to live tadpoles.

Jim McGuire, a herpetologist at the University of California (UC) Berkeley, suggests that the frog species, Limnonectes larvaepartus, is native to the Sulawesi island of Indonesia. The species belongs to the Asian group of fanged frogs. The new species was actually discovered by Djoko Iskandar, an Indonesian researcher, in the 1990. However, the new species was not confirmed as a distinct species until now.

The mating and giving birth process of the frog has still not been observed. The majority of the frogs have external fertilization but this species has internal fertilization.

"This new frog is one of only 10 or 12 species that has evolved internal fertilization, and of those, it is the only one that gives birth to tadpoles as opposed to froglets or laying fertilized eggs," says McGuire.

The researchers are trying to find how male frogs are able to fertilize eggs inside the female as frogs do not have a conventional sexual organ for transferring sperm. The female frogs usually lay eggs and male frogs lay sperm on top of the eggs to fertilize them.

However, a few frog species have evolved a penis-like organ called the tail that transfers sperm in females, who lay the fertilized eggs underneath rocks in streams.

Laying eggs is just one type of reproductive mode. The researchers of the study suggest that some frog species swallow their eggs and breed them inside the body. In one frog species, the male broods the eggs in the vocal sac. Some species of frogs also carry tadpoles and eggs in small pouches on their sides and back.

The researchers reveal that this species of frogs are usually brown or gray in color. The frogs measure about 1.5-inches, or 40 mm, and weigh fewer than 5 grams, or two-tenth of an ounce. Males usually possess a couple of fang-like projections that arise from the lower jaw, which they use while fighting.

The frog species normally live in small puddles and streams in the Indonesian rainforests.

Experts reveal that there are up to 25 species of Limnonectes frogs on the island of Sulawesi; however, only four species have been confirmed so far that includes the latest larvaepartus.

The study has been published in the journal PLOS ONE.