An animal that can breathe through its skin and not through its lungs might sound a little alien-like, but strangely enough, this animal lives on Earth and is known as Barbourula kalimantanensis, the frog without lungs.
The first recorded species of frog that breathes without lungs was found in a clear, cold-water stream on the island of Borneo in Indonesia. It gets all of its oxygen through its skin.
"Nobody knew about the lunglessness before we accidentally discovered it doing routine dissections," study lead author David Bickford, a biologist at the National University of Singapore, said in an email.
His colleague Djoko Iskandar at the Bandung Institute of Technology in Indonesia first described the frog in 1978 from one specimen. About 15 years later, fishermen found another individual.
"Each specimen was deemed so valuable that scientists did not want to sacrifice the animals for dissection," Bickford said.
But the biologist immediately partially dissected several frogs when he found the species on a recent expedition to Borneo.
The researchers suggest lunglessness in B. kalimantanensis may be an adaptation to the higher oxygen content in fast-flowing, cold water.
"Cold water can hold more dissolved oxygen than warm water," Bickford explained.
The frog also has a low metabolic rate, which means it needs less oxygen.
What's more, the species is severely flat compared to other frogs, which increases the surface area of the skin.So biologists are unsure why a few species have entirely gotten rid of the organs, said David Wake, a biologist and expert in amphibian evolution at the University of California, Berkeley.
"This species is so rare that we know next to nothing concerning its biology," he wrote in an email. "But it is aquatic and lives in cold streams and doubtless has low basal metabolic rate.
Thus loss of lungs as an adaptation to the cold, fast-flowing water "seems like a rational hypothesis to me," he said.
Further studies of the frog to test the hypothesis, however, may be hampered by the species' rarity and endangered habitat, according to Bickford and colleagues.