The More the Merrier? A Large Cladistic Analysis of Mysticetes, and Comments on the Transition from Teeth to Baleen

The origin of baleen whales, and their specialized mode of filter-feeding, marks an important event in the evolutionary history of mammals that gave rise to one of the most distinctive groups of animals alive today. Recent years have seen the description of a number of important new specimens, as well as the publication of a large number of phylogenetic analyses. Yet, despite this great effort, a broad consensus on even the most fundamental relationships within this group has so far remained elusive, a fact perhaps most strikingly reflected in the ongoing debate regarding the taxonomic placement of the extant gray and pygmy right whales, as well as the question of the relative closeness of relationship of all the extant members of the mysticete crown group. Here, I present the taxonomically most comprehensive phylogenetic analysis of extinct and extant baleen whales carried out to date, based on morphological data and utilizing both maximum parsimony and Bayesian methodologies. The results of this study were well resolved and consistent across methodologies. Apart from recovering a clade comprising the pygmy right whale, gray whales, and rorquals, a grouping new to morphological analyses but supported by a number of molecular studies, this investigation also revealed the former clade to be more closely related to a large number of extinct species than to right whales, thus contradicting previous notions of a closely related mysticete crown group. In addition, this analysis also identified a novel clade comprising nearly all the described archaic toothed mysticetes from the late Oligocene (about 23-28 Ma) to the exclusion of all toothless mysticetes. This finding is consistent with a basic assessment of the functional morphology of toothed mysticete vision, and may have implications for the evolution of mysticete filter-feeding and the recently proposed interpretation of some of these archaic taxa as transitional forms possessing both teeth and baleen at the same time.