The rich fossil record of rorqual and humpback whales (Cetacea, Mysticeti, Balaenopteridae) is mainly characterized by monotypic genera since genera including more than one species are extremely rare. The discovery of new species belonging to known genera would be of great importance in order to better understand ancestor-descendant relationships and paleobiogeographic patterns in this diverse group. Recent discoveries in the southern North Sea Basin yielded a number of reasonably well preserved fossil balaenopterids from the Late Miocene; this sample includes a balaenopterid skull from Liessel, The Netherlands, which shares key characters with Archaebalaenoptera castriarquati from the Pliocene of Mediterranean. This skull is permanently held by Oertijdmuseum, Boxtel, The Netherlands, with the number MAB002286 and is investigated here.
A detailed comparative anatomical analysis of the skull MAB002286 is performed in order to understand its relationships. The age of the skull is determined by dinocyst analysis of the associated sediment. A paleobiogeographic analysis is performed to understand paleobiogeographic patterns within the balaenopterid clade the new skull belongs to.
Our work resulted in the description of Archaebalaenoptera liesselensis new species. The geological age of the holotype skull is between 8.1 and 7.5 Ma. The phylogenetic relationships of this species reveals that it is monophyletic with Archaebalaenoptera castriarquati from the Italian Pliocene. Moreover, in combination with a more basal species of Archaebalaenoptera from the late Miocene of Peru, our paleobiogeographic analysis suggests that the North Atlantic ocean played a major role as a center of origin of a number of balaenopterid clades including Protororqualus, Archaebalaenoptera and more advanced balaenopterid taxa. From a North Atlantic center of origin, two dispersal events are inferred that led to the origins of Archaebalaenoptera species in the South Pacific and Mediterranean. The distribution of Archaebalaenoptera was antitropical in the late Miocene. The role played by the Mediterranean salinity crisis is also investigated and discussed.