Megabalaena

Megabalaena is an extinct genus of baleen whales in the family Balaenidae, known from the Toyama Formation of Japan, which dates to the late Miocene epoch. The genus contains a single species, Megabalaena sapporoensis, known from a partial skeleton including a partial skull. It likely had a full body length of.

Discovery and naming

The Megabalaena holotype specimen, SMAC 2731, was discovered in October 2008 by Kazuhisa Mori in outcrops of the Toyama Formation on the bank of the Toyohira River in Sapporo of Hokkaido, Japan. The specimen was excavated and collected over the following several years. It comprises a partial skeleton, including the posterior skull and right mandible, bones of the hyoid apparatus, the sternum, 32 vertebrae, most of which were found in articulation, many rib fragments, both scapulae, and much of the left forelimb.
In 2025, Tanaka and colleagues described Megabalaena sapporoensis as a new genus and species of balaenid whales based on these fossil remains. The generic name, Megabalaena, combines the Ancient Greek word μέγας, meaning "large" and "great", with the genus Balaena, the type genus of the family Balaenidae. The specific name, sapporoensis, references the discovery of the holotype in the city of Sapporo.

Classification

In their phylogenetic analysis using implied weighting, Tanaka et al. recovered Megabalaena as a member of the mysticete family Balaenidae, as the sister taxon to a clade containing the extinct taxa Antwerpibalaena and Eubalaena ianitrix and Charadrobalaena. It notably helps to fill a ~9 million-year-old 'ghost lineage' between the oldest known balaenids and all other known fossil balaenids, which are known from much more recent layers. These phylogenetic results are displayed in the cladogram below: