More: The frogs have flattened bodies, shaped more like a cookie than an apple, with plenty of surface area for gas exchange. So they probably get all the oxygen they need through their skin, the researchers will report online April 17 in Current Biology.

The Borneo frog's closest living kin, evolutionarily, lives in the Philippines and does have lungs. That sister species' conventional breathing apparatus supports the idea that the Borneo frog evolved from ancestors with lungs that were later lost them in the highly aerated water, Bickford says. Lungs could even be a disadvantage in white water, making a frog more buoyant and easier for the current to sweep away.