Megabalaena
Extinct baleen whale genus
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Megabalaena (lit. '"large Balaena"') 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 (~9 million years ago). 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 12.7 metres (42 ft).[1]
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| Megabalaena Temporal range: Late Miocene (Tortonian), | |
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| Reconstructed skeleton of the holotype | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Infraorder: | Cetacea |
| Parvorder: | Mysticeti |
| Family: | Balaenidae |
| Genus: | †Megabalaena Tanaka et al., 2025 |
| Species: | †M. sapporoensis |
| Binomial name | |
| †Megabalaena sapporoensis Tanaka et al., 2025 | |
Discovery and naming
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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 (rear) skull and right mandible, bones of the hyoid apparatus, the sternum, 32 vertebrae, most of which were found in articulation (seven cervical (neck) vertebrae, nine thoracic vertebrae, and 16 more posterior vertebrae), many rib fragments, both scapulae, and much of the left forelimb (humerus, ulna, radius, five carpals, three metacarpals, and two phalanges).[1]
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 (mégas), meaning "large" and "great", with the genus Balaena (the bowhead whale), the type genus of the family Balaenidae. The specific name, sapporoensis, references the discovery of the holotype in the city of Sapporo.[1]
Classification
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In their phylogenetic analysis using implied weighting (k=3), Tanaka et al. (2025) recovered Megabalaena as a member of the mysticete (baleen whale) family Balaenidae, as the sister taxon to a clade containing the extinct taxa Antwerpibalaena and Eubalaena ianitrix (known from Belgium)[2][3] and Charadrobalaena (known from Italy).[4] It notably helps to fill a ~9 million-year-old 'ghost lineage' between the oldest known balaenids (Morenocetus and Peripolocetus) and all other known fossil balaenids, which are known from much more recent layers. These phylogenetic results are displayed in the cladogram below:[1]
| Balaenidae |
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