Researchers confirmed that the ichthyosaur fossil discovered in Takahashi City, Okayama Prefecture, is the first ichthyosaur fossil discovered in western Japan. The fossil was buried in rocks from the Late Triassic Period (approximately 220 million years ago) and was confirmed through joint research by Okayama University of Science and other institutions.

Professor Kato carefully observes the ichthyosaur fossils at Takahashi City Hall. Image source: Okayama University of Science

On June 29, the annual meeting of the Japanese Paleontological Society was held at Hokkaido University. Professor Takafumi Kato of the Department of Dinosaur Paleontology officially announced the discovery at the meeting. This is the first time that ichthyosaur fossils have been found in strata from this period in Japan. Paleontologists specializing in ichthyosaurs have emphasized the rarity of such fossils, saying specimens from this period are "extremely rare worldwide."

The fossil is encased in a piece of argillaceous sandstone that is 59 centimeters wide, 34.5 centimeters deep and 26 centimeters high. The rock, which has been on display at the Naruwa Museum of Art in Takahashi City for many years, is thought to be a fossil of the Monotis clam, which is often used as a landmark fossil from the Late Triassic. Museum records show that the rock was part of the museum's collection before it was renovated in 1994 and came from Takahashi City.

The turning point occurred on July 26, 2023, when Professor Kato was conducting a practical education project for junior high school and high school students. During a lecture in the museum's fossil exhibition hall, he and his long-time collaborator Dr. Hirokazu Yukawa of the Fukui Prefectural Dinosaur Museum took a closer look at the rock. That's when they discovered a large bone fragment embedded in the stone. "Wait a minute—that's a bone!" Kato exclaimed. Closer examination revealed its porous, spongy interior surrounded by a thin layer of dense bone—an anatomical feature typical of reptiles adapted to life in the sea. With a background in paleontology, Kato immediately recognized the fossil's potential significance.

To find out how much fossil material it contains, the research team cut a 14-centimetre-thick slab from the rock and examined it using a CT scanner at the Fukui University School of Medicine. They identified 21 bone fragments, including ribs, vertebrae and shoulder blades. The analysis revealed four distinct characteristics:

The vertebrae are thin and have a unique hourglass shape.

Each vertebra has two rib articular surfaces.

The ribs have bangs and are gourd-shaped in cross-section.

The shoulder blades are slender and tapered in the middle.

These features led the team to conclude that the fossil belonged to an ichthyosaur.

So far, all ichthyosaur fossils discovered in Japan, including Utatsu Gyoryu (Utatsusaurus) from the Early Triassic, Kudanohama Gyoryu (Mixosaurus) from the Middle Triassic, and Hosoura Gyoru (Leptopterygius) from the Early Jurassic, were discovered in Minamisanriku Town, Miyagi Prefecture.

From left to right: Dr. Yukawa Koichi, Professor Kato Takafumi and curator Kyoko Ikari are studying Triassic fossil-bearing rocks that led to the discovery of Japan’s first West Japanese ichthyosaur fossil. Image source: Okayama University of Science

Commenting on the discovery, Dr. Ryosuke Motani, an authority on ichthyosaurs at the University of California, Davis, said: "NorianRepresents a key turning point in the evolutionary history of ichthyosaurs, when pelagic species evolved almost entirely from their coastal ancestors. However, ichthyosaur fossils from this period are extremely rare globally, with well-preserved specimens only found in British Columbia, Canada. The fact that they are now found in Japan suggests that these advanced ichthyosaurs may have been able to cross the Pan-ocean, which was even wider than the Pacific today. This is a very important finding. "

The Norian Stage is a stage in the Late Triassic that occurred approximately 227 million to 206 million years ago. At the time, Pangea was a vast global ocean surrounding the supercontinent Pangea.

Before the academic report, the Gaoliang Municipal Government held a press conference. Attendees included Mayor Yoshio Ishida, Professor Kato, Dr. Yukawa, and Kyoko Ikari, Director of the Naruwa Art Museum. Mayor Ishida is looking forward to this discovery, saying: "We hope that follow-up research can yield more results. We see this discovery as an opportunity to promote regional revitalization and stimulate public interest."

Professor Kato emphasized the important role that museums play in preserving local specimens and serving as educational resources. “This discovery was made possible by the Naruwa Art Museum’s ongoing maintenance and management of local materials and its role as an educational platform,” he pointed out. Speaking of the fossil itself, he added: "The shape of the scapula is particularly striking. It may indicate a strong swimming ability, although further detailed analysis is needed. Regardless, this fossil will be a valuable clue to understanding the evolution of ichthyosaurs."

Recalling the moment of discovery, he shared, "I made a habit of looking at rocks and fossils from different angles, always thinking, 'Is there something more here?' It was the first time in over 40 years that I stumbled across something like this. It was truly an unforgettable moment."

The ichthyosaur fossil is scheduled to be on display at the Naruwa Art Museum for about a month during the summer vacation. It promises to be a valuable educational tool, helping children understand the earth's rich history and local cultural heritage.

Compiled from /scitechdaily