Plethodontidae

The family Plethodontidae, commonly named Lungless Salamanders, is the biggest family of salamanders, with more than 370 species spread across the Americas, southern Europe, and Korea (the only Plethodontidae in Korea was discovered only in 2005).

Members of this family have been found in a variety of niches, from full aquatic species to even arboreal species. Uniquely among salamanders, Plethodontidae have narrow grooves between the nostrils and the upper lip, with the males of some species having protuberances on the upper lip. The majority of species are fully terrestrial, laying eggs on the ground, while same have aquatic larvae and terrestrial adults, while others are completely aquatic, preserving larval features.

Their most prominent feature is the lack of lungs, with the animals breathes through their skin and the lining in their mouth.

The main hypothesis on this adaptation is that it is an adaptation to cool, fast flowing mountain streams. Cool mountain streams are rich in oxygen, and for the larvae and adults of the plethodontidae ancestors, lungs may have not only not necessary, but even a disadvantage, as they increase buoyancy and the risk of being swept away by the current.

This hypothesis has been recently disputed, generating some controversy. The main objection to the main hypothesis is based on the assumption that the geography of the Appalachian mountains in the Late Mesozoic is inconsistent with the cool, fast-flowing brooks which were assumed being the origin of the Plethodontidae, and instead the plethodontidae have a semi-aquatic/terrestrial origin.