Relative warps meet cladistics: A contribution to the phylogenetic relationships of baleen whales based on landmark analyses of mysticete crania

Abstract

During the last few years research on fossil baleen whales experienced a renaissance. Several important fossils were described, and new and extended cladistic analyses were performed, partly including molecular data from living species. Despite the progress in our knowledge of their phylogeny, many questions have still not been resolved. A different attempt to illustrate mysticete relationships is presented here using landmark analyses. For the present analysis, 38 dorsal views of mysticete skulls and skull reconstructions were scanned and thirteen landmarks were defined. The method used is the relative warp analysis. This method allows a clustering of elements according to their similarity in shape. The calculated relative warps explain main shape variations in the sample. As in parsimony analyses the toothed mysticetes are clearly distinguishable. Representatives of the Aetocetoidea are grouped very closely together and therefore their classification in this family is strongly supported. The performed analysis shows that the crania of the Balaenidae have developed similarities to the cranium of Janjucetus hunderi. The restriction of the Cetotheriidae to a small group of taxa is confirmed here and includes in this analysis Cetotherium, Mixocetus, Piscobalaena, and Titanocetus with a close relationship to the living gray whale. The stem-balaenopterids do not show any clear signals in the present analysis. There is no support for a subdivision into further families. The structure of the dorsal cranium of Protororqualus and Praemegaptera is very similar to that of Balaenoptera.