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Dinosaur fossil unearthed in west Japan in 2004 identified as new species

OKAYAMA -- A team of researchers in Japan have found that pieces of fossilized dinosaur bones that were unearthed on the west Japan island of Awaji in Hyogo Prefecture in 2004 were from a new species. The dinosaur has since been named "Yamatosaurus izanagii" in a nod to the "Kojiki," or "records of ancient matters," compiled in 712, which mentions the island.

    This artist's rendition by Masato Hattori shows the Yamatosaurus izanagii, left, and the Kamuysaurus japonicus, which coexisted in the same period. (Image courtesy of Okayama University of Science)

    The team consisting of researchers at Hokkaido University, Okayama University of Science and others studied the fossils of mandible and other bones, and concluded that they belonged to a new species of an herbivorous dinosaur, based on its unique dentition characters.

    The fossilized bones of its lower jaw, shoulder and other parts were discovered from the Late Cretaceous stratum dating back some 72 million years ago in the Hyogo Prefecture city of Sumoto in May 2004 by amateur fossil collector Shingo Kishimoto, 72, who lives in the city of Himeji in the same prefecture. Initially, the dinosaur was considered to belong to a species of Lambeosaurinae, a genus of Hadrosauridae, a duck-billed herbivorous dinosaur.

    The research team newly analyzed the fossil in detail. As there were unique features such as there being only a single row of teeth as opposed to other hadrosaurid dinosaurs which had multiple rows, they determined it to be a new species. As part of its shoulder bone was not fully developed, it was found to be a primitive Hadrosauridae species. Its body length is apparently estimated at 7 to 8 meters, and weight at 4 to 5 metric tons.

    Yamatosaurus izanagii's mandible fossil is seen. (Photo courtesy of Okayama University of Science)

    Its scientific name Yamatosaurus izanagii derives form "Yamato," which refers to ancient Japan, and "Izanagi," a male deity that appears in Japanese mythology. Yoshitsugu Kobayashi, a member of the research team and professor at Hokkaido University, explained the reason behind the naming: "It was discovered on Awaji island, which is mentioned as 'the first island created (by deities) in the country' in Kojiki. It is also important when thinking of the origin of hadrosaurids."

    In 2019, the fossilized bones of a hadrosaurid dinosaur's nearly entire body from the Late Cretaceous period that were unearthed in Mukawa, Hokkaido, were certified to be a new species named "Kamuysaurus japonicus." According to the research team, coexistence with the primitive Yamatosaurus and the evolved Kamuysaurus in the same period implies a possibility that Asia was a prosperous area for hadrosaurid dinosaurs. It is apparently rare to discover fossils of different species in sea strata, and the implication that both may have lived near the seashore is also uncommon. Kobayashi said, "We would like to figure out the evolution from Japan's unique viewpoint."

    Hokkaido University professor Yoshitsugu Kobayashi, left, and Okayama University of Science researcher Ryuji Takasaki explain the discovery of a new dinosaur species, as Takasaki holds a replica of a fossilized bone at Okayama University of Science in the city of Okayama on April 26, 2021. (Mainichi/Hanami Matsumuro)

    Kishimoto, who discovered the fossil, said: "I'm grateful for the result thanks to the researchers' efforts over a long time. I also like the name ' Yamatosaurus,' which is easy to pronounce and familiar to the Japanese people."

    Their study was published in the British online journal Scientific Reports on April 27.

    (Japanese original by Hanami Matsumuro, Okayama Bureau)

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