Megabalaena

Not to be confused with Megabalanus, a genus of barnacles.

Megabalaena Temporal range: Late Miocene (Tortonian), 9.4–8.6 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
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

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]

Discovery and naming

Map of the type locality in Japan (left) and photographs of the holotype excavation (right)

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

Speculative life restoration

Size compared to a human

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

†Morenocetus parvus †Peripolocetus vexillifer †Megabalaena sapporoensis †Antwerpibalaena liberatlas †Charadrobalaena valentinae †Eubalaena ianitrix †Archaeobalaena dosanko †Balaenula astensis †Balaenella brachyrhynchus †Balaena ricei †Balaena montalionis Balaena mysticetus (bowhead whale) Eubalaena japonica (North Pacific right whale) Eubalaena australis (Southern right whale) Eubalaena glacialis (North Atlantic right whale) †Eubalaena shinshuensis

References

1. Tanaka1, Yoshihiro; Kimura, Toshiyuki; Shinmura, Tatsuya; Ohira, Hiroto; Furusawa, Hitoshi (2025-08-20). "A new member of a large and archaic balaenid from the Late Miocene of Sapporo, Hokkaido, Japan partly fills a gap of right whale evolution". Palaeontologia Electronica. 28 (2): 1–59. doi:10.26879/1549. ISSN 1094-8074.
2. de Lavigerie, Guillaume Duboys; Bosselaers, Mark; Goolaerts, Stijn; Park, Travis; Lambert, Olivier; Marx, Felix G. (2020-07-17). "New Pliocene right whale from Belgium informs balaenid phylogeny and function". Journal of Systematic Palaeontology. 18 (14): 1141–1166. Bibcode:2020JSPal..18.1141D. doi:10.1080/14772019.2020.1746422. ISSN 1477-2019.
3. Bisconti, Michelangelo; Lambert, Olivier; Bosselaers, Mark (2017-06-27). "Revision of "Balaena" belgica reveals a new right whale species, the possible ancestry of the northern right whale, Eubalaena glacialis, and the ages of divergence for the living right whale species". PeerJ. 5 e3464. doi:10.7717/peerj.3464. ISSN 2167-8359. PMC 5490463. PMID 28663936.
4. Bisconti, M.; Chicchi, S.; Monegatti, P.; Scacchetti, M.; Campanini, R.; Marsili, S.; Carnevale, G. (2023). "Taphonomy, osteology and functional morphology of a partially articulated skeleton of an archaic Pliocene right whale from Emilia Romagna (NW Italy)". Bollettino della Società Paleontologica Italiana. 62 (3): 231–262. doi:10.4435/BSPI.2023.09 (inactive 11 July 2025).