Molecular evidence for the monophyly of flatfishes (Carangimorpharia: Pleuronectiformes).

Proliferation of phylogenetic studies based on poor taxonomic sampling or insufficient molecular evidence usually leads to conflicting results. As a consequence, advancement of systematic knowledge yields to confusion. The problem is exacerbated for taxonomic groups with historically difficult resolution of evolutionary relationships such as the flatfishes. Molecular evidence to support monophyly for this emblematic group of fishes and their interrelationships has been elusive, and a recent paper published in this journal went as far as to claim that flatfish monophyly can be rejected with molecular data, implying that the asymmetric body plan unique to these fishes had two independent origins. A reanalysis of this evidence suggests the contrary and combination of the new data with existing datasets unequivocally supports the monophyly of this group based on analyses of concatenated data as well as species tree approaches. Resolution of difficult phylogenetic problems requires analysis of larger datasets with adequate taxonomic coverage and sound hypothesis-testing procedures. Proliferation of partial studies claiming extraordinary results should be avoided in order to advance the field of molecular phylogenetics.