Two amateur collectors stumbled upon the find of their lives when they discovered the first and oldest fossil bird in Japan during a walk near a reservoir in a small town in the island nation.

After they shared their mysterious find with paleontologists at Hokkaido University, brothers Masatoshi and Yasuji Kera found they had discovered an iconic marine diving bird of the late Cretaceous, found often in the Northern Hemisphere but rarely in Asia.

Heralded as the “first report of the hesperorinthiforms from the eastern margin of the Eurasian Continent" and the "best preserved hesperornithiform material from Asia," the find included nine skeletal elements from one individual, including the thoracic vertebrae and the femoral bones.

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"This amazing find illustrates the special relationship paleontologists and other scientists have with ordinary citizens who come upon interesting and unusual objects," said Tomonori Tanaka, a Ph.D. student at the Department of Natural History Sciences, Hokkaido University.

Tanaka also co-authored the report "The oldest Asian Hesperornithiform from the Upper Cretaceous of Japan, and the phylogenetic reassessment of Hesperornithiformes," which was published on the Journal of Systematic Palaeontology website Tuesday.

Estimated to be somewhere between 90 million to 84 million years old, the bones are now housed at the Mikasa City Museum in Hokkaido.

Given the name Chupkaornis keraorum, referring to the indigenous Hokkaido chupku meaning “eastern” and the Kera brothers who discovered it, the fossil bird sported a unique combination of characteristics.

With a “finger-like projected tibiofibular crest of femur; deep, emarginated lateral excavation with the sharply defined edge of the ventral margin of that the thoracic vertebrae (those vertebrae in the upper back); and the heterocoelous articular surface of the thoracic vertebrae,” Chupkaornis will provide details about the evolution of this group of diving birds, according to a press release by Perot Museum of Nature and Science, Dallas.

Chupkaornis keraorum Amateur collectors in Japan are credited with the discovery of the country's first and oldest fossil diving bird, it has been named Chupkaornis keraorum. Scientific reconstruction by Japanese paleo-artist Masato Hattori. Photo: Illustration by Masato Hattori

“In Japan, many important vertebrate fossils have been discovered by amateurs because most of the land is covered with vegetation, and there are few exposures of fossil-bearing Cretaceous rocks. This research is a result of collaboration with amateurs, and I am thankful to their help and understanding of science,” Yoshitsugu Kobayashi, who also co-authored the report, said.

One of the most widely distributed birds in the Cretaceous of the northern hemisphere, hesperornithiformes had extremely reduced forelimbs and powerful hindlimbs. This suggests the bird was a flightless, diving one and also had teeth.

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Anthony Fiorillo, curator and vice president of research and collections at the Perot Museum of Nature and Science, is considered one of the world’s preeminent experts on Arctic dinosaurs, given his decades of research in Alaska. He is also fascinated by the Beringia land bridge that connected North America to Asia till about 11,000 years ago.

Having been members of his field teams during Alaskan expeditions, Kobayashi and lead-author Tanaka asked Fiorillo to collaborate on the discovery.

“This study not only tells important new information about the evolution of this unusual group of birds, it also helps further our understanding of life in the ancient northern Pacific region, more specifically what was going on in the ocean while dinosaurs walked the land,” Fiorillo said.