Adaptations that puzzle scientists and hopefully engage both imagination and intellect of the younger generation. Lunglessness in salamanders of the family Plethodontidae is one such innovation. This adaptation was so successful, in fact, that it accounts for two thirds of all salamander species. We will now explore one of the competing hypotheses on how this phenomenon might have evolved. And since all non-plethodontid salamander larvae have lungs, buoyancy seems their most logical purpose when all gas exchange is being performed by the gills and skin.
Most carbon dioxide is released through the skin in all salamanders.
Such animals would be readily displaced downstream and out of their environment. On the other hand, lungless larvae and larvae with reduced lungs would tend to sink to the stream bottom where they could establish and maintain their position against the water current. The cold, swift, and thus well oxygenated waters would have further facilitated the switch from lungs to skin. Thus, emerging terrestrial adults would be completely reliant on cutaneous gas exchange due to adaptations of the larval form, a theory which held up for nearly 70 years before recently being challenged. Thus, Appalachian stream habitats have not been stable since the mid-Mesozoic, a fundamental assumption to the long held scenario.