Photo/IllutrationFossils discovered in Kushimoto, Wakayama Prefecture, have been identified as coming from the head of a baleen whale that died 16 million years ago. (Provided by the Wakayama Prefectural Museum of Natural History)

KAINAN, Wakayama Prefecture--Fossil fragments discovered in 1973 in a coastal town came from the head of a baleen whale that existed 16 million years ago, a study showed.

Researchers at the Wakayama Prefectural Museum of Natural History in Kainan said the whale, estimated at about 7 meters in length, was likely among the largest of the species at that time.

Yukio Sako, now a 66-year-old fossil collector, found the fragments in a rock in a geological layer beneath a beach in the town of Kushimoto, Wakayama Prefecture, 45 years ago.

He later donated the rock containing the fossils to the museum.

Fossil fragments together measuring 110 centimeters by 50 cm were part of the mammal’s skull, while those from the lower jawbone were about 90 cm in length in total, the researchers said.

The whale lived about 16 million years ago after the dinosaur extinction, according to the researchers.

Following a three-year project to retrieve the fossils from the rock, the museum in 2017 started a joint study on the fragments with the Osaka Museum of Natural History and Gunma Museum of Natural History.

A researcher at the Wakayama Prefectural Museum of Natural History said the discovery shows that baleen whales were becoming larger.

“The one discovered is around midsize by today’s standards, but it was among the largest baleen whales back then,” the researcher said.

The findings were carried in the online edition of the English journal of the Paleontological Society of Japan.

The fossils will be on display at the museum through Dec. 28.