May 28 2014

12:00 LSB 2320

Annalisa Berta
Department of Biology, San Diego State University

New insights into the systematics, evolution and feeding anatomy of baleen whales New insights into the systematics, evolution and feeding anatomy of baleen whales


Despite renewed interest and intensive study several aspects of the phylogeny of mysticetes (baleen whales) remain controversial among which is the position of enigmatic “cetotheres” as either stem or crown mysticetes. In part, this conflict is a result of differing phylogenetic signals (i.e. morphology vs molecular data). A new hypothesis is presented for “cetotheres” using the largest morphologic data set to date (53 extinct and 12 extant taxa and more than 200 characters). Preliminary results support “cetotheres” as positioned within crown mysticetes which has implications for the reconstruction of feeding evolution in baleen whales.

The bulk filter feeding niche exploited today by mysticetes was likely occupied in the past (170-65 Ma) by now-extinct bony fish and plankton-feeding sharks and rays using gill rakers as filters instead of baleen. Study of the ontogeny and morphometrics of baleen, a novel keratinous structure that makes up the filter feeding apparatus of mysticetes, reveals that the longest, widest and thickest baleen plates are found toward the posterior half of the rack, providing the greatest filtration area. The transition from teeth to baleen, a major macroevolutionary transition that enabled bulk filter feeding by mysticetes, is investigated within a phylogenetic context. Evidence from tooth genes indicates frameshift mutations present in the mysticete genome that corroborate their ancestral toothed heritage. The stepwise evolution of feeding suggests a common ancestral suction feeding strategy among both baleen and toothed whales. Raptorial feeding using well developed teeth characterizes early stem toothed mysticetes (i.e. mammalodontids) 28-30 Ma with other contemporaneous stem taxa (i.e. aetiocetids) likely possessing both teeth and baleen. A combination of latex injection, CT and dissection confirm that baleen receives blood from vessels within the superior alveolar arteries via the lateral palatine foramina. Later diverging crown mysticetes show morphological modifications (i.e. unsutured mandibular symphysis, bowed jaws, throat grooves and ventral throat pouch) that increase the size of the oral cavity and facilitated bulk feeding. Future phylogenetic and anatomical study is needed to determine whether skim feeding seen in balaenids (right whales) arose before or after the evolution of engulfment feeding in balaenopterids. Resolution of relationships among “cetotheres” is key to unraveling further details of feeding evolution in crown mysticetes.











































































































































































































































































































































































































































































































































































































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