The complete skeleton of Nipponosaurus sachalinensis kept at the Hokkaido University Museum

The fossils were found on Sakhalin Island in 1934 by a Japanese team on what was then Japanese territory. It was quickly named Nipponosaurus sachalinensis and declared a separate species from closely related dinosaurs around Europe and North America.

In ensuing decades, the claim became a bit controversial, since the skeletal remains presented a bunch of conundrums, especially since it was a juvenile dinosaur that would have had changing bones as it grew older. It also looked very similar to other fossils that had already been named.

Now, another Japanese team from Hokkaido University claims they have definitively proven the dinosaur is its own taxon, they announced in a paper in the journal Historical Biology.

“Our study clarified the phylogenetic status of Nipponosaurus, and we are now interested in the relationship between Nipponosaurus and other Japanese dinosaurs, whose fossils have been unearthed one after another in recent years,” said Ryuji Takasaki, a graduate student and lead author. “We aim to discover how diverse dinosaurs inhabited East Asian coastal areas.”

The new claim was made after the Hokkaido scientists dissected three of the fossilized bones found in 1934. They delineated the vascular canals in the thigh bone, along with the growth rings in the bones.

For comparison, they investigated the same traits in the very closely related Hypacrosaurus from North America.

Their conclusion: the Nipponosaurus showed enough differences, even among the juvenile specimens, to be a completely separate species. Those unique identifiers include a shelf-like structure on the lower jaw, and extremely short front legs.

Their theory: Nipponosaurus is a hadrosaurid like its similar cousins dug up elsewhere on the globe, but is more primitive than originally thought – and one that migrated from Europe to Eastern Asia.