• Bayesian phylogenetics
• historical biogeography
• killifishes
• long-distance dispersal
• timetree

The teleostean order Cyprinodontiformes comprises over 1200 species of mainly fresh and brackish water fishes, commonly known as killifishes, distributed all over the world (with the exceptions of Oceania and Antarctica). Although many species are especially well known due to their role as model organisms (especially for developmental and evolutionary biology) and to their popularity as aquarium fishes, relatively few studies have tried to reconstruct the broad phylogenetic history of the whole order, and a consensus is yet to be reached on the evolutionary relationships between the 10 families currently recognized within the order. The intercontinental distribution of killifishes is particularly interesting, considering that only few derived species can live in a marine coastal environment; this has been often interpreted as the result of continental drift, and especially of the fragmentation of Gondwana, the southern supercontinent. However, the oldest killifish fossils are much more younger than the Gondwanan fragmentation, and, recently, many studies have been pointing out the importance of rare and stochastic long-distance dispersal events in shaping the present biogeographic distribution of many vertebrate clades (including even freshwater fishes).
The aim of this study was to reconstruct the phylogenetic history of the order Cyprinodontiformes and to give a reliable timescale for its origin and radiation, in the interest of testing contrasting biogeographic hypotheses that could explain the widespread geographical distribution of the group. In order to do so, a Bayesian phylogenetic analysis has been performed using five molecular nuclear markers for 135 different species; multiple primary fossil calibrations from the literature has been used to reconstruct a time-calibrated tree. After that, ancestral geographic areas for nodes of interests have been reconstructed under different parametric biogeographical models, and the best-fitting model among them was chosen according to their likelihood. Additionally, maximum likelihood ancestral-state reconstruction has been done for some key ecological and life-history characters (habitat and developmental strategies).
The phylogeny reconstructed in this study suggests that the current classification of killifishes in ten different families is in need of a revision, as some of these families may represent non-monophyletic groupings. Moreover, the results show that the order Cyprinodontiformes probably originated in the Late Cretaceous, after the major breakups of Gondwana, hinting at a fundamental role of long-distance dispersal in the biogeographic history of this clade.