Reviewing morphological characters in light of new molecular phylogenies – the caudal fin skeleton of Ovalentarian taxa

The Ovalentaria is a taxon of teleosts which has only recently been
proposed on the basis of molecular-genetic analyses. Multiple, previously
widely-separated fish families are assembled with this taxon. For the
first time, the Ovalentaria are analysed using a comparative morphological
approach. The caudal fin skeleton of 355 species covering all 48
ovalentarian families are examined in cleared and stained specimen, µCT
datasets and x-ray images. A total of 38 morphological characters are
evaluated and used for ancestral character state reconstructions and
phylogenetic analyses. Results provided phylogenetic hypotheses for the
relationships of ovalentarian taxa and a grundplan of the caudal fin
skeleton of the last common ancestor of all Ovalentaria. An evolutionary
trend towards the reduction of skeletal elements in the caudal fin can be
observed. Furthermore, a connection between the evolution of the caudal
skeleton and the modes of locomotion found in ovalentarian taxa is
discussed. The phylogenetic analyses provided convincing topologies that
are highly in agreement with molecular-genetic based hypotheses.