Baleen Whale Fossils Found in Akita Prefecture May Link to Modern Whales

The Yomiuri Shimbun

7:00 JST, November 11, 2023

NOSHIRO, Akita — Fossilized bones from a baleen whale found in Noshiro, Akita Prefecture, may back up the theory that the creatures started growing much bigger about 2.6 million years ago, according to experts.

Researchers believe the fossils might provide valuable data linking this whale to the large whales that exist today.

Officials from Shinshu University and the Fukui Prefectural Dinosaur Museum, which are excavating the fossils, showed the site to the media on Nov. 1.

A team led by paleontology expert Katsura Yamada, a professor at Shinshu University’s Faculty of Science, has been examining areas along the Taneume River in Noshiro for small microfossils of microorganisms since 2019. In 2020, the team discovered the partly exposed fossil of a mammal along a tributary of the river. Yamada contacted Hiroto Ichishima, a whale researcher and deputy director of the museum, and they began a joint excavation of the site.

The fossils reportedly were found in a stratum formed about 2.7 million years ago, and they include a lower right jawbone about four meters long, four ribs about two meters long, and what could be a shoulder blade. Shell fossils were found on the surface of the fossils, indicating that the area had been covered by shallow water at the time.

Based on the jawbone’s size, the researchers estimated the whale was about 18 meters long. “This would make it a larger class even among baleen whales,” Ichishima said. Baleen whale bones from around the same period have been discovered in Hokkaido, but this is the first such lower jawbone to be found in Japan.

Modern-day baleen whales include the blue whale, which can exceed 30 meters in length, and the fin whale, which can reach 18 meters to 24 meters long. According to Ichishima, there is research indicating that baleen whales grew much larger around the boundary of the Pliocene and Pleistocene periods about 2.6 million years ago. The whale uncovered in Noshiro appears to be from the end of the Pliocene.

“This will provide us with valuable data about the evolution of baleen whales,” Ichishima said.

The fossils are scheduled to be temporarily stored at the former Taneume Elementary School, before being transported to the dinosaur museum in Fukui Prefecture for further research.