Evolution and Diversification of Delphinid Skull Shapes

The diversity of the dolphin family was established during a short window of time. We investigated delphinid skull shape evolution, mapping shapes on an up-to-date nuclear phylogeny. In this model, the common ancestor was similar to Lagenorhynchus albirostris. Initial diversification occurred in three directions: toward specialized raptorial feeders of small prey with longer, narrower beaks, e.g., Delphinus; toward wider skulls with downward-oriented rostra and reduced temporal fossae, exemplified by suction feeders, e.g., Globicephala; and toward shorter and wider skulls/rostra and enlarged temporal fossae, e.g., Orcinus. Skull shape diversity was established early, the greatest later developments being adaptation of Steno to raptorial feeding on large prey and the convergence of Pseudorca toward Orcinus, related to handling large prey. Delphinid skull shapes are related to feeding mode and prey size, whereas adaptation to habitat is not marked. Over a short period, delphinid skulls have evolved a diversity eclipsing other extant odontocete clades.