Origin of the Mediterranean rajid fauna: contribution of molecular and biogeographic data

The family Rajidae (skates and rays) has the highest species diversity among chondrichthyan fishes. The rajids are distributed in all oceans, with many endemic species. In the NE Atlantic Ocean and the Mediterranean Sea, rajid fauna includes 32 nominal species with nine endemic species (four in the NE Atlantic and five in the Mediterranean). This biogeographical pattern suggests that the present rajid faunas likely originated from ancestral forms existing at the beginning of the Tertiary by multiple species radiation processes at the regional level. Alternatively, in some case, palaeogeographical and palaeoclimatic data suggested that present rajid species could be elements of relict faunas (i.e. the Antarctic fauna). Here, through the phylogenetic analysis of biogeographic and mitochondrial DNA data, we obtained evidence for: 1) a recent origin and rapid dispersal of the Mediterranean fauna, since the present species diversity seems to be arisen in a relatively narrow time window extended from Middle Miocene to Early Pleistocene, likely by speciation processes related to dramatic geological and climatic events in the Mediterranean, and 2) a Gondwanic evolutionary and dispersal pattern of the family that is compatible with the young age of the Mediterranean fauna. A biogeographic and molecular research project focussing on the phylogeny and evolution of the Eastern Atlantic rajid regional faunas will be carried out to empirically validate the Gondwanic origin and dispersal of Rajidae.