The Unknown Dinosaurs of Japan
by Tetsuhiro Hagiwara
When you think of the word "dinosaur," what kind come to mind?
You may think of the major dinosaurs that you’ve seen in the movie "Jurassic Park," such as the most fearsome carnivorous dinosaur, Tyrannosaurus rex, which is known to everyone, Triceratops, which has three horns and can compete with carnivorous dinosaurs, and Brachiosaurus, one of the largest dinosaurs in the world, which stretches out its long neck to eat leaves from tall trees.
Until recently, I was one of those people who only could recall these most popular ones, but my five-year-old son's fascination with dinosaurs gave me a chance to learn about Japanese dinosaurs, which I had never heard of before. I would like to introduce Japanese dinosaurs at this time.
The most famous Japanese dinosaur is Fukuiraptor, which was discovered in Fukui Prefecture in 2000. The first dinosaur fossil to be found in Japan was of a Sauropod in Iwate Prefecture in 1978. Since then, there have been 9 species of dinosaurs, like Fukuiraptor, that have been given scientific names as endemic to Japan.
In Japan, dinosaurs have been discovered one after another since 2000, and a fossil named "Yamatosaurus isanagii" in April this year (discovered in 2004) is now attracting attention from around the world as it holds the key to the evolution of dinosaurs that flourished for a long time.
The fossils, including bones of part of the lower jaw, were discovered in a 72-million-year-old stratum in Sumoto City in southern Awaji Island. The maximum length is estimated to be about 8 meters and the weight about 5 tons. The Hadrosauridae, also known as platypus dragons, were the most prosperous plant-eating dinosaurs of the Cretaceous period, with flat duck-like beaks.
Now, what's great about this dinosaur is that Yamatosaurus is a primitive species of Hadrosauridae, which emerged in the middle of the Cretaceous period (about 95 million years ago) and is expected to reveal the evolutionary process of Hadrosauridae. Compared to the evolved species of the Late Cretaceous period, the shoulder muscles were underdeveloped, suggesting that the transition from bipedal to quadrupedal walking occurred during the transition from primitive to evolutionary individuals. In other words, the change in walking style may have led to the expansion of their behavioral range, which in turn led to the diversification and prosperity of the species.
The coastal areas of East Asia, including Japan, will be important in analyzing this possibility in the future. A fossil of a Yamatosaurus, which may have been a primitive species about 95 million years ago, has been discovered in a 72-million-year-old stratum. This suggests that the East Asian coast, including Japan, was a "Refugia," a region where species were able to survive in their original state. It is interesting to note that Yamatosaurus coexisted with evolved species for 20 to 30 million years without going extinct, and I am sure I am not the only one who thinks it is a dreamy story that its descendants thrived for 20 million years without going extinct.
In July of this year, it was also announced that five eggshell fossils of theropod (bipedal carnivorous dinosaur) Troodontidae were discovered in the Tedori Group in Takayama City, Gifu Prefecture. The fossils were found in the stratum of the Early Cretaceous Period, about 130 million years ago, and are believed to be the oldest dinosaur eggshell fossils in Japan. Since no bone fossils of the Troodontidae family have been found in the world so far, the research team of Tsukuba University, which discovered the fossils, said, "It is significant that we have shown the possibility of the existence of unknown dinosaurs in the Tedori Group.”
Troodon and eggshell fossils from tsukuba.ac.jp
As you can see, new species and world-class discoveries of Japanese dinosaurs are being made one after another, so why not keep an eye on them?
As a side note, did you know that Japan has one of the world's three largest dinosaur museums*, the Fukui Prefectural Dinosaur Museum? My family visited the museum in the spring of this year with my son's enthusiasm. It was a wonderful museum where even non-enthusiasts could make fresh discoveries. The exhibition volume, including 44 dinosaur skeletons, is worthy of the name "World's Three Greatest Dinosaurs," and as it is a famous place for real-time fossil excavation, you can see the know-how of fossil excavation, actual work scenes, etc. Although it has been suspended due to the recent Corona pandemic, there are also event facilities nearby where visitors can experience fossil excavation and hotels with nice rooms called "dinosaur rooms."
It is a funny story that our son, a few months after the trip, quickly switched his interests from his favorite dinosaur to Pokémon.
*The rest of them are the Royal Tyrrell Museum of Paleontology in Canada and the Jigong Dinosaur Museum in China.
Fukui Prefectural Dinosaur Museum
Hotels with dinosaur rooms
Troodon and eggshell fossils from tsukuba.ac.jp