The evolution of lunglessness in tetrapods (amphibians, reptiles, birds, and mammals) is an exceedingly rare event. So far lunglessness is known to occur only in amphibians, in particular two families of salamanders 1, 2 and a single species of caecilian [3]. Here, we report the first case of complete lunglessness in a frog, Barbourula kalimantanensis, from the Indonesian portion of Borneo (Figure 1A). Previously only known from two specimens 4, 5, a recent expedition to central Kalimantan on Borneo rediscovered two new populations of this enigmatic aquatic frog (Figure 1B,C). This allowed for a more comprehensive assessment of the species' ecology and anatomy that led to the discovery of its lack of lungs. Loss of lungs in Amphibia is most likely due to their evolutionary history at the interface between aquatic and terrestrial habitats and their ancient ability to respire through the skin [5].
