Megabalaena sapporoensis was a member of the balaenid baleen whale lineage, related to modern right whales and bowhead whales. Living in marine waters covering what is now northern Japan during the late Miocene, about 9 million years ago, it helps to fill in a significant gap in the fossil record of this group.
Known from a partial skeleton about 12.7m long (~42′), it was much larger than earlier balaenids, but smaller than modern forms. It also had a narrower flipper shape compared to its modern relatives, a less arched jaw, and its neck vertebrae were only partially fused.
Modern right whales are slow-swimming ram feeders, but since Megabalaena was less specialized for this particular filter feeding style it’s unclear what its ecology was.
References:
- Buono, Mónica R., et al. “The early Miocene balaenid Morenocetus parvus from Patagonia (Argentina) and the evolution of right whales.” PeerJ 5 (2017): e4148. https://doi.org/10.7717/peerj.4148
- Tanaka, Yoshihiro, et al. “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 (2025): 1-59. https://doi.org/10.26879/1549
- Wikipedia contributors. “Megabalaena” Wikipedia, 24 Aug. 2025, https://en.wikipedia.org/wiki/Megabalaena