Washington - (Reuters) - A rare and primitive frog living in a remote Borneo stream has no lungs and apparently absorbs oxygen through its skin.
The aquatic frog has evolved backwards, re-acquiring a primordial trait, David Bickford of the National University of Singapore and colleagues reported.
"The evolution of lunglessness in tetrapods (amphibians, reptiles, birds, and mammals) is exceedingly rare, previously known only from amphibians -- two families of salamanders and a single species of caecilian (blindworm)," they wrote.
"Here we report the first case of complete lunglessness in a frog, Barbourula kalimantanensis, from the Indonesian portion of Borneo."
The frog may be endangered because of mining activity, the researchers said.
"The discovery of lunglessness in a secretive Bornean frog, supports the idea that lungs are a malleable trait in the Amphibia, the sister group of all living tetrapods. Amphibians maybe more prone to lunglessness since they readily utilize other methods for gas exchange," they wrote.
Only animals with small body sizes, slow metabolisms and living in fast-flowing cold water where oxygen and carbon dioxide are exchanged quickly may be able to survive without lungs, the researchers said.
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