A vertebrate fossil discovered in a rock from the Late Triassic period (approximately 220 million years ago) in Takahashi City, Okayama Prefecture, has been confirmed through joint research by Okayama University of Science and other institutions to be the first ichthyosaur fossil ever found in western Japan. The discovery was announced by Professor Takafumi Kato of the Department of Dinosaur Paleontology and his research team at the Palaeontological Society of Japan’s annual meeting, held at Hokkaido University. This marks the first time an ichthyosaur has been identified from strata dating to this period in Japan. Experts in ichthyosaur research have called attention to the find, noting that ichthyosaur fossils from this era are “exceptionally rare worldwide.”
The fossil was embedded in a block of muddy sandstone measuring 59 cm wide, 34.5 cm deep, and 26 cm high. The rock had been on display at the Nariwa Museum of Art in Takahashi City as a fossil of Monotis, a Late Triassic index fossil bivalve. Records show the specimen had already been on display prior to the museum’s 1994 renovation and was known to have been sourced from Takahashi.
On July 26, 2023, while leading an educational field program for middle and high school students, Professor Kato, along with his longtime colleague Dr. Hirokazu Yukawa of the Fukui Prefectural Dinosaur Museum, happened to glance at the side of the rock during a lecture in the museum’s fossil gallery — and noticed a sizable bone fragment embedded in it. “Wait — that’s a bone!” he exclaimed. Upon closer inspection, he observed a porous structure typical of spongy bone, with a very thin layer of compact bone — features characteristic of marine-adapted reptiles. With his expertise in paleontology, Professor Kato quickly realized the significance.
Wondering how much fossil material was inside, the team cut a 14 cm-thick slab from the rock and examined it using a CT scanner at the University of Fukui’s School of Medical Sciences. They confirmed 21 bone fragments, including ribs, vertebrae, and a scapula. Their analysis revealed four distinct characteristics:
- The vertebrae were thin and had a distinctive hourglass shape.
- Each vertebra featured two rib articulation surfaces.
- The ribs were grooved and had a gourd-shaped cross-section.
- The scapula was slender and constricted in the middle.
These features led the team to conclude that the fossil belonged to an ichthyosaur.
Until now, 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 — had been found in Minamisanriku, Miyagi Prefecture.
Commenting on the discovery, Dr. Ryosuke Motani, a leading authority on ichthyosaurs from the University of California, Davis, stated:
“The Norian age represents a critical transition in ichthyosaur evolution, when open-ocean species were nearly fully developed from their coastal ancestors. However, ichthyosaur fossils from this era are extremely rare globally, with well-preserved examples only known from British Columbia, Canada. The fact that one has now been found in Japan suggests that these advanced ichthyosaurs may have been capable of crossing the Panthalassic Ocean, which was even larger than today’s Pacific. This is a highly significant finding.”
The Norian is a stage of the Late Triassic spanning approximately 227 to 206 million years ago. The Panthalassic Ocean was the massive global ocean that surrounded the supercontinent Pangaea during that time.
Before the academic presentation, a press conference was held at Takahashi City Hall. Among those present were Mayor Yoshio Ishida, Professor Kato, Dr. Yukawa, and Nariwa Museum of Art curator Kyoko Ikari. Mayor Ishida expressed his enthusiasm for the discovery, stating, “We’re hopeful that continued research will lead to even more findings. We see this discovery as an opportunity to stimulate regional revitalization and public interest.”
Professor Kato emphasized the importance of the museum’s role in preserving local specimens and serving as an educational resource. “This discovery was made possible because the Nariwa Museum of Art has continuously maintained and managed regional materials, and because it functioned as an educational platform,” he noted. Speaking about the fossil itself, he added, “The shape of the scapula is particularly telling. It may indicate a high swimming ability, though further detailed analysis is needed. In any case, this fossil will serve as a valuable clue in understanding ichthyosaur evolution.”
Reflecting on the moment of discovery, he shared:
“I’ve made it a habit to look at rocks and fossils from different angles, always thinking, ‘Is there something more here?’ After doing this for over 40 years, this is the first time I’ve stumbled upon something like this. It was truly an unforgettable moment.”
The ichthyosaur fossil is scheduled to be on display for about a month at the Nariwa Museum of Art during the summer break. It is expected to be a valuable educational tool, helping children learn about both Earth’s profound history and their local heritage.