Bornean Flat-headed Frog

The Bornean flat-headed frog (Barbourula kalimantanensis) is the only known species of frog in the world that has completely lost its lungs. It relies entirely on cutaneous respiration, meaning it absorbs oxygen directly through its skin.

Because it lacks lungs, this small frog breathes directly through its highly vascularized skin. To make this process efficient, it lives in cold, fast-flowing, highly oxygenated streams in the Kalimantan region of Borneo.

The frog's incredibly flattened head and body increase its overall surface area, which allows for a greater volume of oxygen to be absorbed through its skin. This aerodynamic shape also helps it avoid being swept away by the strong river currents in its habitat.

The species is currently classified as Endangered on the IUCN Red List. Its extremely limited range is under severe threat from illegal gold mining, deforestation, and increased sedimentation in its river habitats.