Putting fish fossils in trees: using advanced phylogenetic methods to co-estimate the phylogeny and temporal diversification patterns of living and fossil Gobioidei

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Gobioids are small benthic fishes that constitute one of the largest suborders of teleost fishes, with about 2200 extant species. They form a significant component of shallow marine, estuarine and freshwater ecosystems and are particularly attractive for studying evolutionary processes because they display numerous adaptations. However, little is known about their evolutionary history despite the availability of a good fossil record comprising about 25 species based on skeletons and about 60 species based on isolated otoliths (ear stones). The objective of the proposed project is to use morphological characters of gobioids to link fossil and living taxa in a unified, time-scaled phylogeny and infer their history of diversification. A matrix will be prepared based on skeleton, scale and otolith characters for all known fossil taxa and for representatives from all living families and lineages, with apogonids and kurtids as outgroups; available molecular data will be added for the extant species. Special attention will be given to the identification of phylogenetic informative otolith characters because otoliths have never before been used in phylogenetic analyses. Parsimony, maximum-likelihood and Bayesian analyses will be performed (i) for the morphological data, (ii) for the morphological data in combination with the DNA sequence data, and (iii) by adding available DNA sequence data from taxa not represented in the morphological dataset. The outcome will be analysed using fossil constrained "tip-dating", which is a novel method for assessing phylogenetic node ages. Traditional phylogenetic dating methods use fossils only as date calibrations; the fossils are not included directly in the dated phylogeny. In tip-dating, fossil specimens with coded morphological data are included as tips in the tree, along with DNA and morphology from specimens of living species. The phylogenetic relationships of the fossils and living species are then estimated simultaneously with the dates of speciation events in the tree. Tip-dating the gobioid tree will establish a new temporal framework for gobioid evolution. Several groups are currently studying the molecular phylogeny and evolution of gobioids, and our combination of fossil and molecular data will be an exciting approach to significantly advance this field of science. Moreover, this project will be one of the first major tip-dating studies, and will get a lot of attention as a result.