Article: The salamander Brachycormus noachicus from the Oligocene of Europe, and the role of neoteny in the evolution of salamanders
All available material of the late Oligocene salamandrid amphibian Brachycormus noachicus is redescribed, with a reconstruction of its skeleton and an evaluation of its range of variation. This neotenous salamandrid is strikingly similar, in the shape of its visceral skeleton, to larvae of the contemporary Triturus in the final stages of metamorphosis, and to neotenous specimens of Triturus alpestris. However, in contrast to the latter facultative neotenous larvae, Brachycormus, though morphologically underdeveloped, was fully ossified. Occurrence of neoteny in the Tertiary tailed amphibians was associated with the global deterioration of climate during the Oligocene (a significant drop of mean annual temperatures and a broader range of annual temperatures). Prolongation of cold meant that larvae were not able to metamorphose in time and thus became permanent water dwellers. Subsequent improvement of climate in the Miocene permitted the amphibious life-cycle to resume; this was accompanied by completion of metamorphosis of the visceral skeleton but retarded osteogenesis in other respects (e.g. incomplete frontotemporal arch). Thus, Brachycormus may be taken as a phylogenetic link between the Oligocene Caudata related to Chelotriton and the contemporary genus Triturus.