New Delhi (PTI): Scientists claim to have found the first complete lungless aquatic frog in Indonesia 30 years after its existence was first mooted.

Two new populations of Barbourula kalimantanensis, the flat-headed aquatic frog, were found by a team of researchers during a recent expedition to Kalimantan in Indonesia.

"People have been trying for 30 years. But when we did and I was doing the initial dissections right there in the field, I have to say that I was very skeptical at first. It just did not seem possible," David Bickford of the National University of Singapore said.

"We were all shocked when it turned out to be true for all the specimens we had from Kalimantan," he added. The findings were published in the April 8 issue of science journal 'Current Biology'.

The animal, whose natural habitat is tropical and sub-tropical moist lowland forests and rivers, is believed to carry out its entire respiration by the skin.

This finding is expected to boost the study of evolutionary science.

"Complete loss of lungs is a particularly rare evolutionary event that has probably only occurred three times," Bickford said.

Previously absence of lungs was reported in only two other specimens known to science -- salamanders and single species of caecilian, a limbless amphibian resembling an earthworm.

"Loss of lungs might be an adaptation to a combination of factors -- a higher oxygen environment; the species presumed low metabolic rate; severe flattening of their bodies that increases the surface area of their skin; and selection for negative buoyancy, meaning that the frogs would rather sink than float in water," the researchers said.

"The thing that struck me most then and now is that there are still major firsts to be found out in the field. We knew that we would have to be very lucky just to find the frog," Bickford said.

Despite the interesting finding, the scientists express concerns about further studies on the "remarkable frog" which is threatened by rapid habitat loss.

Pointing out that further studies of this species' might be hampered by its rarity and endangerment, Bickford said: "This is an endangered frog that we know practically nothing about, with an amazing ability to breathe entirely through its skin."

The researchers strongly encouraged careful conservation of remaining habitats of the species that is considered to be evolutionary sister group to all other tetrapods.