Photo/IllutrationMasato Tajima, who with his son discovered the whale fossil in Tokyo, sits, right front, in front of the reassembled fossilized skeleton. (Provided by the Akishima city education board)

  • Photo/Illustraion
  • Photo/Illustraion
  • Photo/Illustraion
  • Photo/Illustraion

The skeleton of a prehistoric whale that caused a sensation when it was discovered by a father and a son on a Tokyo riverbed in 1961 has finally been identified as a previously unknown species from 2 million years ago.

Found in the city of Akishima, in the southwestern area of the Tokyo metropolis, it was nicknamed “Akishima kujira” (Akishima whale), and the fossil became a mascot of the city.

But instead of the almost complete skeleton being proudly put on display, it was given no scientific name and left to gather dust for five decades in storage at the Shinjuku office of the National Museum of Nature and Science.

Apparently, there was “no researcher to study it,” but that all changed when in March 2012, due to the relocation of the Shinjuku office, it was transferred to the collection of the Gunma Museum of Natural History.

There the whale was introduced to a certain Toshiyuki Kimura and it finally got the attention it deserved ... and a proper name.

Kimura, a researcher at the museum in Gunma Prefecture, published a paper on the skeleton Jan. 1 in Paleontological Research, an academic journal published in English by the Paleontological Society of Japan. He also gave it an official scientific name, eschrichtius akishimaensis, after the name of the city where it was discovered.

The fossilized skeleton was discovered on the riverbed of the Tamagawa river in Akishima’s Ogamicho district in August 1961 by Masato Tajima and his son, Yoshio, who is now 61.

It was 12 meters long and is estimated to be about 2 million years old based on the age of the stratum it was unearthed from.

Kimura says the Akishima whale is related to an existing species of gray whale, eschrichtius robustus, that inhabits the northern Pacific and other areas. It belongs to the same eschrichtius genus based on its skeletal features, including a large nasal bone and a lower jaw, which suggest a smaller muscle in that region. That means it is the oldest fossil of the genus worldwide.

However, differences in its skull show it is a different species. For example, whereas the gray whale’s nasal bone has a pointy tip, the Akishima whale’s bone is square, and the shapes and positions of the maxillary and forehead bones were also different to those of the gray whale.

“(The fossilized skeleton) is proof that there was once a lineage of whale that is different to today’s gray whale,” said Kimura, emphasizing the significance of the fossil. “The Akishima whale will become the type specimen, and is an important specimen in the study of the evolution of the whale genus.”

Yoshio Tajima, the "boy" who found it with his late father all those years ago, said he almost “gave up” hope that its true identity would ever be discovered.

“I am truly happy that it was found out to be a new species,” said Yoshio.

He found the fossil when he and his father were searching the riverbed for fossils of shells and fish.

The finding attracted huge attention nationwide with city government officials setting up a security tent near the excavation site to ward off potential thieves who might creep in under the cover of darkness, Yoshio said.

Then, as the decades passed with the whale mothballed, the number of Akishima residents who do not know about the whale has increased. To maintain local enthusiasm, Yoshio has been actively promoting the unique fossil. He has held workshops, encouraged people to visit the site and held photo exhibitions relating to the discovery.

“I think my father is pleased to hear that the whale has the word ‘Akishima’ in its name,” said Yoshio. “I reported it to him by displaying a copy of Kimura’s paper on the Buddhist altar.”

Masahiko Ito, chief of the social education department of the Akishima city government, said: “The name of Akishima has now become global. I am emotional that it is, finally, officially recognized.”

Akishima city has long promoted itself as a “city of whale,” even if many people had started forgetting about why that was so.

Cartoon whales are selected as its mascots and it has Kujira matsuri (whale festival) and Kujira Park named after the whale.

The story about the fossil also features in reading material for social study classes at local elementary schools.

The city government is also now planning to exhibit a life-size replica of the skeleton in a new educational facility that is due to open in March 2020. A 2-meter-long model of the whale and a piece of the actual fossil are also in the display plan.

“We hope to make the most of the Akishima whale once again to increase the charm of our city to locals as well as to people living outside,” said Ito.

A promotional event is also scheduled for the next fiscal year.