A molecular timescale for the evolution of the African freshwater fish family Kneriidae (Teleostei: Gonorynchiformes)

We re-examine the phylogenetic relationships of the family Kneriidae using whole mitogenome sequences across all four kneriid genera including the two recently recognized species of Cromeria (C. nilotica and C. occidentalis), and we provide a timescale to discuss the evolution of the family. The resulting phylogeny supports the monophyly of the family Kneriidae and the monophyly of the genus Cromeria. The two Cromeria species exhibit large genetic divergence (18.2%) that is comparable to those between Grasseichthys gabonensis and each two Cromeria species (16.9 and 19.0%). The three paedomorphic kneriid species (C. occidentalis, C. nilotica and G. gabonensis) do not form a monophyletic group, but the alternative hypothesis in which they are monophyletic cannot be statistically rejected. Two alternative relaxed molecular-clock Bayesian analyses, differing on how we time-calibrated the phylogenetic tree using the fossil record, support a Late Jurassic or Late Cretaceous origin of the African freshwater gonorynchiforms. The early diversification of the family Kneriidae is concomitant with the reductions or loss of several morphological characters that took place in a relatively short time interval of about 12-21 million years either during the Eocene or at the end of the Late Cretaceous.