KATSUYAMA, Fukui -- A fossil that was discovered in 1965 in the city of Shimonoseki in Yamaguchi Prefecture has been confirmed as being a genuine dinosaur egg fossil of a possible new species, an investigation team said on June 5.
The discovery is significant because until recently, it had been assumed that a fossilized bone belonging to a "Moshiryu" dinosaur -- found in the Iwate prefectural town of Iwaizumi in 1978 -- had been the first postwar discovery of a dinosaur fossil in Japan. "This discovery will result in Japanese dinosaur research history being rewritten," an expert explained.
Fossilized remains of a hadrosaurid dubbed Nipponosaurus were discovered in 1934 in what was at the time the Japanese territory of Karafuto, on Sakhalin island in present-day Russia.
The investigation team that verified the authenticity of the dinosaur egg fossil consists of organizations such as the Fukui Prefectural Dinosaur Museum. According to the museum, the dinosaur egg fossil was found on Sept. 20, 1965 in an upstream area of the Ayaragi River in the city of Shimonoseki by then-high school student Yoshiharu Shimizu and his friend. Shimizu took photographs and drew sketches of the fossil, which he kept together with the fossil itself at his home.
Many years later, in 2016, Shimizu asked the Mine Municipal Government in Yamaguchi Prefecture -- where his nephew works -- to carry out an appraisal. Subsequently, the Fukui Prefectural Dinosaur Museum, Fukui Prefectural University and Mine Fossil Museum jointly looked into the authenticity of the fossil.
The dinosaur egg fossil is broken into eight pieces, with the respective diameters ranging between 2 to 7 centimeters. The thickness of the shell, for all the pieces, is about 3.7 millimeters. It is not known how many eggs the pieces have derived from. Judging from the thickness of the shell, and the crystal structure, it is thought to bear similarity to the "theropod" dinosaur egg, which has been found in China and Mongolia. Furthermore, it is believed that the egg was from a relatively large dinosaur, and is different to the eight types of dinosaur egg fossils that have been found so far in Japan.
Below the discovery site, which has been paved as a result of bank protection work, lies stratum that was formed 100 to 120 million years ago, during the Lower Cretaceous Period. There is a high chance that the dinosaur egg fossil dates back to this era.
The dinosaur egg fossil will be on display at the Fukui Prefectural Dinosaur Museum during a special exhibition between July 14 and Oct. 15, 2017.