Nipponosaurus (Japanese lizard)
Nipponosaurus (Japanese lizard)
Named By : Takumi Nagao - 1936
Diet : Herbivore
Size : Estimated 4 meters long
Type of Dinosaur : Euornithopod
Type Species : N. sachalinensis (type)
Found in : Russia, Sakhalin
When it Lived : Late Cretaceous, 89-84 million years ago
Nipponosaurus, which means “Japanese Lizard”, is a lambeosaurine-horsaur that was found in sediments from the Yezo Group and Sinegorsk on Sakhalin Island, Russia. It was part of Japan at the time it was named. N. sachalinensis is the only known species. It was named after a single juvenile specimen that Takumi Nagao discovered in 1934. Additional material from the same individual was found in 1937. The taxon has been ignored and doubted since then. Synonymy with other Asian hadrosaurs has been suggested, as well as status of a nomen Dubium. However, redescriptions in 2004 and 2017 have confirmed that the species is distinct. Although it was difficult to date the single specimen, it is possible that the species lived somewhere in the upper Santonian and lower Campanian around 80 million years ago.
The holotype (UHR6590, University of Hokkaido Register) was found during construction of a hospital to treat the Kawakami Colliery of the Mitsui Mining Company in Karafuto Prefecture (now Sinegorsk Sakhalin, Russia). It was broken up when it was discovered. Professor Takumi Nagao of Imperial University of Hokkaido named N. sachalinensis and described it in 1936. Nippon is the Japanese name for Japan. The first dinosaur to be named after a discovery on Japanese territory was N. sachalinensis. However, South Sakhalin was annexed in 1945 by the Soviet Union. Sakhalin is the specific name.
Although the specimen was complete at the time it was discovered, much of its skull and limbs were missing. In 1937, a second expedition was organized. The holotype-related limb material was then recovered. Nagao wrote a second article about the species in 1937, describing these additional remains.
Nipponosaurus was originally described as a Trachodontidae member. However, Trachodon is now an invalid nomen dubium. This family is now called the Hadrosauridae. Nagao believed it to be the closest taxa Cheneosaurus or Tetragonosaurus to its relatives. This suggests that his species may have been congeneric with one. These were later found to be juvenile Hypacrosaurus Corythosaurus, Lambeosaurus and Lambeosaurus forms and not separate species.
The taxon was not mentioned for the rest of the 20th century. They were still valid species. However, their relationship with Cheneosaurus (the Cheneosaur) and Procheneosaurus (the Procheneosaurus) was accepted. After this, it was seldom assigned beyond the Lambeosaurinae. In 1967, Nipponosaurus was given a humerus taken from Japan’s Hashima Island. It was also known as Trachodon. The specimen has not been recognized by any further studies and the referral was ignored. However, the species is still believed to be represented only by one specimen. A 1977 review of Asian dinosaur paleontology identified it as a close relative to Mandschurosaurus. A 1989 study found that the metacarpals of this dinosaur could have indicated a basal position within Hadrosauridae. A 1994 review of Japanese dinosaurs revealed that many Asian hadrosaurs were incomplete. This could indicate that some of them (including Nipponosaurus) may actually be representative of the same species.
In the 21st Century, more extensive research was conducted. The 2004 redescription of the species focused on its growth stage. It was determined to be a valid taxon and the holotype was still immature. A 2017 study added more details to the specimen and performed a microscopic exam on sections of the left and right femurs, ribs, and an isolated, unattached chevron. This confirmed the age of holotype.