Evolutionary history of Balaenidae

The living species of the family Balaenidae are experiencing a very high extinction risk. Knowledge of their evolutionary history may be helpful in conservation strategies. In this paper a review and osteological diagnoses for the genera and species of the Balaenidae is given. Also palaeoecological features are determined, like the evolution of a large body size, changes in species composition and changes in the choice of reproductive sites over the last five million years. Finally, an overview of the problems encountered in balaenid conservation is made. The family Balaenidae includes two living genera and three or four species depending on the systematic treatment that is preferred (morphology-based or molecular-based). Here, a review of the fossil record of Balaenidae is given, and the validity of several taxonomic names, based on the revision of type materials held in some European institutions, is assessed. From the comparative analyses of this paper, it is concluded that Balaenula praediolensis, Balaena paronai, Balaena primigenius, and Balaena etrusca represent indeterminate Balaenidae genera. Emended osteological diagnoses for the remaining valid taxa are provided: the genus Eubalaena (including two or three living species: E. glacialis, E. australis, and, possibly, E. japonica), the genus Balaena (including two species: B. montalionis and B. mysticetus), the genus Balaenula (including three species: B. balaenopsis, B. astensis, and B. sp. nov. from Japan), the genus Balaenotus (including one species: B. insignis). The phylogenetic analyses of Balaenidae, that have been published over the past few years, are revised and a consensus view, based on both molecules and morphology, is proposed. Three themes in the palaeoecology of Balaenidae are assessed: the evolution of large body size, changes in species composition in Pliocene-to-Recent balaenid assemblages, and changes in balaenid preference in choosing reproductive sites over the last five million years. Palaeobiogeographic works on Balaenidae are reviewed based on the distribution of the fossil taxa and recent molecular works. A general overview of the problems encountered in balaenid conservation is made in light of phylogenetic works based on molecular divergences and the fossil record.