A comparative atlas of selected skeletal elements of European urodeles (Amphibia: Urodela) for palaeontological investigations

The osteology of European urodeles was studied extensively in the past, but comparative analyses of isolated bones are rare, despite being the most useful tool for the identification of fossil remains. The present work is focused on the most robust skeletal elements (therefore, common in the fossil record: otic–occipitum complexes and vertebrae) and provides taxonomically significant diagnostic characters at the genus level for European genera of urodeles, including some taxa whose osteology was poorly known (e.g. Euproctus and Calotriton). Characters subject to wide variability are identified, and their use is discouraged for diagnoses of extinct species. A selection of diagnostic characters is used herein to build an identification key for each studied skeletal element and for a phylogenetic analysis to understand whether these osteological elements can convey a genuine signal. The analysis under Bayesian inference resulted in a well-supported Salamandridae clade and Pleurodelinae tribe. Salamandrina was recovered as part of the Pleurodelinae, in agreement with previous morphological phylogenetic analyses, but in contrast to the conclusion of molecular studies.