Ray-finned fish evolution during the breakup of Pangaea: the Halecomorphi

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The geographic and climatic changes produced by the breakup of Pangaea during the Mesozoic directly influenced the evolution of vertebrates. In particular, the faunas of ray-finned fishes changed dramatically. At the beginning of this Era, ray-finned fishes were phylogenetically diverse and well represented by all known actinopterygian major clades (Cladistia, Chondrostei, Ginglymodi, Halecomorphi, and Teleostei). Numerous lineages within these clades went extinct by the end of the Mesozoic and actinopterygians developed into the nearly monophyletic modern fish faunas, composed mostly by teleosts (~33.000 living species vs. 14 spp. cladistians, 29 spp. chondrosteans, 7 spp. ginglymodians, and only one halecomorph). After more than two centuries of research and despite the efforts of the relatively few specialists in contrast to other fields of palaeontology, we still know very little about the tempo and mode of Mesozoic actinopterygian evolution and not even the phylogenetic relationships between and within the major clades of Actinopterygii are well understood. According to a recent study, climate change had been the main driver of actinopterygian macroevolution at least since the Late Jurassic. However, this study does not include sufficient taxa representing the main groups of Mesozoic ray-finned fishes, most of which went extinct by the end of this Era. Was climate change a major driver of the extinction of those lineages? Which are the rates of speciation and extinction, trait evolution and diversification in those extinct lineages? These and many other questions remain to be answered. The so-called ‘phylogenetic comparative methods’ (PCMs) are powerful tools to explore these and other palaeobiological issues, but they require robust phylogenetic hypotheses. With the ultimate aim to study macroevolutionary processes in ray-finned fish evolution during the Mesozoic through the application of PCMs, a series of projects have been planned to provide solid phylogenetic grounds to allow the application of these methods. Amongst them, this proposal is dedicated to the Halecomorphi. With a single living species, the bowfin, several aspects make the Halecomorphi particularly interesting from the macro-evolutionary point of view. Halecomorph fishes were very abundant and diverse during the Mesozoic, in particular in the Jurassic of nowadays Europe, which was subjected to significant geographic changes during that time, including the development of rich marine platforms and temporary epicontinental seas. Jurassic halecomorphs are ecologically varied, including fast-swimming predators like tunas, demersal opportunistic feeders very similar to the living bowfin, and numerous small-sized species of more generalized trophic morphology. Numerous species are known, but their high-level taxonomy and phylogenetic relationships are controversial. Therefore, this project is aimed to solve the systematics of these fishes using rigorous phylogenetic methodology.