Abstract

As the largest known vertebrates of all time, mysticetes depend upon keratinous sieves called baleen to capture enough small prey to sustain their enormous size. The origins of baleen are controversial, with one hypothesis suggesting that teeth were lost during a suction-feeding stage of mysticete evolution and that baleen evolved thereafter. Here we report a new species of toothed mysticete, Coronodon havensteini, from the Oligocene of South Carolina that is transitional between raptorial archaeocete whales and modern mysticetes. Although the morphology and wear on its anterior teeth indicate that it captured large prey, its broad, imbricated, multi-cusped lower molars frame narrow slots that were likely used for filter-feeding. Coronodon havensteini is a basal, if not the most basal, mysticete, and our analysis suggests that it is representative of an initial stage of mysticete evolution where teeth were functional analogues to baleen. In later lineages the diastema between teeth increased, in some cases markedly so and may mark a stage where the balance of the oral fissure shifted from mostly teeth to mostly baleen. When placed in a phylogenetic context, our new taxon indicates that filter-feeding was preceded by raptorial feeding, and that suction-feeding evolved separately within a clade removed from modern baleen whales