Phylogenetic implications of skull structure and feeding behavior in balaenopterids (Cetacea, Mysticeti)

Abstract

Balaenopteridae actively feed by engulfment. They swim rapidly at their prey (40-50 km/h), with their mouth open and their lower jaw pulled wide open at a 90° angle. Their mouth and ventral pouch engulf up to 60 m3 of water, then the mouth closes and food is swallowed after the expulsion of water through the baleen. These highly specialized feeding mechanisms are associated with a developed ascending process of the maxilla and a hooklike and outwardly bent coronoid process of the dentary. These features participate in the strengthening of the architecture of the skull and jaw. Although all fossil baleen mysticetes bear a developed coronoid process, only 6 taxa (Piscobalaena nana, Cetotherium rathkei, Herpetocetus sendaicus, Metopocetus durinasus, Mixocetus elysius, and Nannocetus eremus) have a posteromedially expanded ascending process of the maxilla. Feeding strategies and mechanisms of each extant family of baleen whales are compared and correlated with the associated skull and dentary features. This correlation suggests a preliminary phylogeny of the mysticetes and a new definition of the Cetotheriidae sensu stricto (Piscobalaena nana, Cetotherium rathkei, Herpetocetus sendaicus, Metopocetus durinasus, Mixocetus elysius, and Nannocetus eremus).