GATESY, J.**; DEMERE, T.; MCGOWEN, M.; BERTA, A.; U. C. Riverside; San Diego Natural History Museum; U. C. Riverside; San Diego State U.: Stepwise Evolution of Filter Feeding in Baleen Whales
Synthesis of molecular and paleontological data can offer unique insights into the history of complex adaptations. Here, we use a combined phylogenetic analysis of morphological traits and sequence data from the mitochondrial and nuclear genomes to track a major evolutionary transformation in Mysticeti (baleen whales). The origin of baleen and the loss of teeth are correlated with the evolution of obligate filter-feeding in mysticete whales. The transition from tooth-bearing jaws to the edentulous, baleen-lined upper jaws of extant mysticetes, however, was not accomplished in a single evolutionary step. New evidence from the late Oligocene toothed mysticete Aetiocetus weltoni documents the presence of palatal nutrient foramina in this archaic taxon; similarly placed palatal foramina house vessels that nourish baleen in extant mysticetes. In the context of our combined phylogenetic analysis, these observations suggest that baleen existed in concert with functional teeth in Aetiocetus and likely other basal Mysticeti. To supplement the fossil data, we sequenced three genes critical to the production of dentine/enamel from extant mysticetes and outgroup taxa. Enamelin and ameloblastin, which are expressed in developing enamel tissue of mammals, have nonsense mutations in several baleen whale lineages and apparently are non-functional. Simultaneous phylogenetic analysis of paleontological and molecular data implies that early toothed mysticetes evolved baleen and that the mineralized adult dentition was subsequently lost over a span of several million years in one clade of Mysticeti, resulting in extant baleen whales which are left with degenerate enamel genes and rudimentary, embryonic tooth buds.