Do you know the creature called an “ichthyosaur”?
It was a “member of the reptile group” that appeared about 250 million years ago, before the first dinosaurs came into being, and had a body shape very similar to a dolphin’s.
From Saturday, August 2 to Sunday, August 31, 2025, a special exhibition was held to commemorate the discovery of the first ichthyosaur fossil in western Japan among the fossils in the collection of Nariwa Museum.
We heard about the rock containing the actual ichthyosaur fossil on display and the circumstances of its discovery, and are reporting on it here.
The information presented was current when this article was published in October 2025. Please note that it may differ from current information.
Introduction to the Fossil Exhibition Room at Nariwa Museum
Nariwa Museum opened in 1953 as Okayama Prefecture’s first town-run art museum, to honor the legacy of Kojima Torajiro, a Western-style painter from Nariwa-cho. Since then, it has hosted numerous special exhibitions in addition to its permanent exhibition.
The current building is the third, newly constructed in 1994 to a design by world-renowned architect Ando Tadao. The modern concrete building, with its exposed concrete characteristic of Ando’s architecture, is like a work of art both inside and out.
The “Fossil Exhibition Room,” in one corner of the museum’s second floor, displays many fossils, mainly plant fossils collected nearby.
An art museum and a fossil exhibition. The reason for this slightly unusual combination lies in the geological strata of the Nariwa area.
Strata dating back about 230 million years extend across the Nariwa area. Plant fossils are collected from these strata, making this a region where academic research has been active from the Meiji period to the present day.
For this reason, fossils have been exhibited since the museum opened in 1953, with the aim of preserving and collecting the region’s natural heritage.
What are ichthyosaurs?
What kind of creature was the “ichthyosaur,” discovered for the first time in western Japan?
Ichthyosaurs are considered to have appeared on Earth about 250 million years ago, during the Triassic Period of the Mesozoic Era. They were members of the reptile group and looked very similar to dolphins.
Because their names are similar, they are often confused with dinosaurs, but they are entirely different creatures. The Mesozoic Era was a time when reptiles adapted to life in the sea appeared, and ichthyosaurs were one such group.
Exhibition highlights
This special exhibition was held in a corner by the entrance to the Fossil Exhibition Room.
Centered on the rock containing the ichthyosaur fossil, the exhibition used panels and models to clearly explain ichthyosaurs and the significance of this discovery.
Here is the actual rock containing the ichthyosaur fossil that was on display.
To extract the fossil, unnecessary parts are first roughly removed, then the surface is gradually scraped away to expose the fossil little by little. The photo shows an intermediate stage; the fine white lines visible on the surface are marks left by the tools used to scrape the rock.
A local visitor who came to see the exhibition during our visit remarked, “Fossils turn up in the hills behind my house.” This gave us an idea of how rich the Nariwa area is in fossils.
A model made with a 3D printer based on X-ray CT scan data of the rock was also on display. There was also a comparison with dolphin bones, which are very similar in appearance and shape. The differences between ichthyosaurs and marine mammals were clearly explained, making it very informative.
Interview: On the discovery of the ichthyosaur fossil
We spoke with Ikari Kyoko, curator in charge of fossils at Nariwa Museum, about the special exhibition and the circumstances surrounding the discovery of the ichthyosaur fossil.
Could you tell us how the ichthyosaur fossil was discovered?
Ikari (honorific omitted)
In the summer of 2023, two years ago, Professor Kato of Kurashiki University of Science and the Arts at the time (now at Okayama University of Science) and Researcher Yukawa of the Fukui Prefectural Dinosaur Museum visited our museum with students for a tour.
While looking at the various fossils on display in the museum, Professor Kato noticed something.
He said, “Wait, isn’t that a bone?” Researcher Yukawa and I checked it there and then and confirmed that it was a bone. After that, we examined the bone and determined that it was an ichthyosaur fossil.
Could you tell us about the significance of this discovery?
Ikari
Until then, ichthyosaur fossils had been discovered in Japan only once, in Minamisanriku Town, Miyagi Prefecture.
The discovery in Nariwa was the second in Japan and the first in western Japan, making it highly significant academically.
Although the fossils are from different periods, an ichthyosaur fossil was also discovered in Chiba Prefecture from the same period as the Nariwa fossil, so the two are treated together as the second discovery.
The ichthyosaur fossil discovered in Nariwa dates to the “Norian” of the Late Triassic, about 220 million years ago. It was the first ichthyosaur fossil from this period to be discovered in Japan.
Many diverse kinds of ichthyosaurs existed throughout the Mesozoic Era. As a result, although ichthyosaur fossils have been found in large numbers around the world, fossils of ichthyosaurs from the Late Triassic are relatively rare.
Even when they are discovered, many are only fragmentary, and many ichthyosaurs remain poorly understood as a whole.
For that reason, I believe this discovery is also important for understanding the evolution of ichthyosaurs.
I understand that after the exhibition, the ichthyosaur fossil will be taken to Fukui Prefecture for research. What kind of work is being done there?
Ikari
In Fukui Prefecture, the main work is analysis using nondestructive testing with X-ray CT (computed tomography).
We have learned that the rock containing this fossil is extremely hard, making it difficult to remove the fossil by cutting away the rock. So, we use X-ray CT to image the fossil inside the rock and obtain detailed data on the fossil (bones).
Nondestructive testing using X-ray CT has been carried out before, but going forward, we hope to obtain more detailed information.
Could you tell us about what comes next?
Ikari
We will continue to build on the new information through analyses such as the X-ray CT analysis mentioned above, and compile our findings into academic papers. I believe we will make further discoveries along the way.
We plan to share our findings with everyone as they become available, so we hope you will follow our progress.
From the Writer
Through this reporting, I learned that the Nariwa area has long been a place where fossils are frequently found, and that the ichthyosaur fossil was discovered through a combination of various coincidences.
When I think about how many fossils of unknown ancient creatures may still remain in Nariwa’s geological strata, it feels like something out of a grand adventure.
After its exhibition at Nariwa Museum ended, the ichthyosaur fossil was also featured in a special exhibition at Okayama University of Science Dinosaur Museum from September 13 to 27, 2025.
We’ll continue to keep a close eye on the many discoveries that future research will bring to light.
Dinosaur-Era Marine Reptile “Ichthyosaur Fossil” Special Exhibition (held August 2–31, 2025) Information
| Name | Dinosaur-Era Marine Reptile “Ichthyosaur Fossil” Special Exhibition (held August 2–31, 2025) |
|---|---|
| Dates | Saturday, August 2–Sunday, August 31, 2025 9:30 a.m.–5:00 p.m. |
| Location | 1068-3 Shimohara, Nariwa-cho, Takahashi City, Okayama Prefecture |
| Admission (tax included) | Admission fees vary by exhibition. Please check the current exhibition information for details. |
| Website | Nariwa Museum |
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