About Nipponosaurus
| Scientific Name (Genus) | Nipponosaurus |
| Meaning of Name |
Japanese lizard
Nippon (Japan) [Place name] - saurus (lizard) [Greek] |
| Classification | Ornithischia, Ornithopoda (Hadrosauridae, Lambeosaurinae) |
| Total Length | Approx. 4m (Estimated to reach over 7.5m as an adult) |
| Diet | Herbivorous |
| Period | Late Cretaceous (Santonian to early Campanian) |
| Sub-classification / Species Name | Nipponosaurus sachalinensis |
| Year of Paper Publication | 1936 |
| Genus Name Publication |
Nipponosaurus Sachalinensis : A New Genus and Species of Trachodont Dinosaur from Japanese Saghalien.
Journal of the Faculty of Science, Hokkaido Imperial University. Ser. 4, Geology and mineralogy, 3(2), 185-220. by Nagao, Takumi 1936. |
Characteristics and Ecology of Nipponosaurus
The skull of Nipponosaurus was equipped with a highly advanced feeding system unique to hadrosaurids. This is a structure called a "dental battery" where hundreds of teeth grow closely together like a stone wall. It had a mechanism where old teeth were constantly pushed out and replaced by new ones, and it is thought to have efficiently ground up and eaten hard Late Cretaceous plants.
Also, there was a small, hollow dome-shaped "crest" on top of its head. It is speculated that this was an organ for communication with peers or for producing resonating sounds.
The leg bone (femur) developed a deep, tunnel-like groove for muscle tendons to pass through. By acting like a pulley, this structure prevented the strong tendons from dislocating, allowing them to run stably even when fleeing from predators such as carnivorous dinosaurs.
The discovered specimen is small, measuring about 4m in total length, but a bone histology study published in 2017 revealed that this individual was a growing young (subadult) that had only hatched 2 to 3 years prior. If it had lived out its natural life and fully grown, it is estimated that it would have become a large dinosaur reaching over 7.5m in total length.
It is a cutting-edge research method that involves cutting a very thin slice of dinosaur bone and observing its internal structure under a microscope. By counting the "lines of arrested growth" carved into the bone like the rings of a tree, it is possible to estimate with high accuracy how old the dinosaur was when it died.
Phylogenetic Classification and Evolutionary History
For many years, Nipponosaurus was thought to be a close relative of North American dinosaurs (such as Hypacrosaurus), and it was believed to have migrated to Asia after evolving in North America (North American origin hypothesis).
However, a phylogenetic analysis was conducted that excluded the unique characteristics (noise) of immature young individuals and compared only the pure species characteristics. As a result, it turned out that Nipponosaurus is not a North American dinosaur, but a more primitive lambeosaurine very closely related to dinosaurs like Blasisaurus discovered in European (Spanish) strata.
With this discovery, the "Eurasian Eastward Expansion Hypothesis" has been proposed, suggesting that their ancestors originated around Europe and crossed the vast Eurasian continent eastward over tens of millions of years, eventually reaching the Far East around Sakhalin and Japan.
History of Discovery and a Strange Fate
Source: Nipponosaurus Sachalinensis : A New Genus and Species of Trachodont Dinosaur from Japanese Saghalien.
Journal of the Faculty of Science, Hokkaido Imperial University. Ser. 4, Geology and mineralogy, 3(2), 185-220.
by Nagao, Takumi 1936.
Nipponosaurus was discovered in 1934, before World War II, at a hospital construction site inside the Kawakami coal mine facility in Sakhalin, which was a Japanese territory at the time (now part of Russia).
The excavation was led by Professor Takumi Nagao of Hokkaido Imperial University, and it was described in a paper in 1936. This became the first case of a dinosaur being described based on a fossil discovered within its own territory by a Japanese researcher, marking the origin of Japanese dinosaur research.
Interestingly, Nipponosaurus, a terrestrial herbivorous dinosaur, was discovered in a marine stratum (Upper Yezo Group) and in a state of preservation where about 60% of the entire body was intact. The "Bloat and Float" model is considered the most likely explanation for why it was found in the sea.
The carcass of a dinosaur that died on the coast or along a river is washed out to sea by floods or other events. During the drifting process, putrefaction by bacteria inside the body progresses, generating a large amount of gas. This gas acts as a float, allowing the carcass to drift at sea for a long time. Eventually, when the abdomen bursts and the gas escapes, the carcass sinks to the seabed, is rapidly buried in mud, and goes through the process of fossilization.
Nipponosaurus followed a strange fate thereafter. With the end of World War II, Sakhalin became Soviet territory, and Japanese researchers lost access to the excavation site. Furthermore, because the discovered specimen was an "immature young individual," overseas researchers considered it "just looking at a child of another dinosaur, not an independent species," and it spent a long period of obscurity with its details unknown.
However, entering the 21st century, researchers conducted thorough re-studies utilizing the latest technologies such as CT scans and the aforementioned bone histology. As a result, its unique anatomical features were proven, and it achieved a revival to its status as a valid independent dinosaur.
Museum Exhibitions
The actual fossil (holotype specimen) of Nipponosaurus, which is the starting point of dinosaur research by Japanese people, is still carefully preserved in the storage of the Hokkaido University Museum.
In addition, to widely convey the appearance of this historically and academically extremely important dinosaur, a full-body skeletal restoration (replica) precisely produced incorporating the latest research results is on permanent exhibition at the following major museums.
- Hokkaido University Museum (Sapporo, Hokkaido): One of the main exhibits conveying the historical significance of the university where it was discovered.
- National Museum of Nature and Science (Ueno, Taito-ku, Tokyo): Exhibited as a specimen symbolizing the history of Japan's first dinosaur excavation.
- Fukui Prefectural Dinosaur Museum (Katsuyama, Fukui): Exhibited as a core for learning about the diversity of Asian dinosaurs.