A rare and primitive frog living in a remote Borneo stream has no lungs and apparently absorbs oxygen through its skin, researchers reported on Wednesday

The aquatic frog has evolved backwards, re-acquiring a primordial trait

Studying the frog could help shed light on how lungs evolved in the first place

The frog may be endangered because of mining activity, the researchers said

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