By NAMI SUGIURA/ Staff Writer
February 6, 2023 at 17:44 JST
A fossilized dinosaur eggshell discovered in Mifune, Kumamoto Prefecture, is believed to be close to Coralloidoolithus egg genus. (Provided by Mifune Dinosaur Museum)
MIFUNE, Kumamoto Prefecture--Fossils excavated here about 20 years ago were confirmed to be dinosaur eggs, the first such findings in the Kyushu region, a museum said.
They were the also first discoveries of egg fossils from the Late Cretaceous Period (100.5 million to 66 million years ago) in Japan, the Mifune Dinosaur Museum said on Feb. 4.
The species of the dinosaurs are unknown.
Museum officials said one of the fossils is 27 millimeters long, 10 mm wide and 1.7 mm thick, and the other is 25 mm long, 15 mm wide and 2 mm thick.
If spherical, the eggs would have been about 5 to 7 centimeters in diameter and the size of a baseball.
The museum found one fossil in 2001 and the other in 2003 during excavations in a stratum about 90 million years old downstream from the Amagimi Dam in Mifune.
The stratum contains many fossils of dinosaurs and other reptiles, including turtle eggs.
The fossil excavated in 2003 was stored as a turtle fossil because of its plate-like shape and thickness.
But in autumn last year, researchers examined the cross-sectional structure in detail with a microscope and found the fossil closely resembled the Coralloidoolithus egg genus reported from Cretaceous Period stratum in China.
The recent study also determined the other fossil was also an eggshell.
Dinosaur fossils have been found in more than 40 locations in Japan. However, egg fossils have been discovered in only five strata from the Early Cretaceous Period, including one in Tanba, Hyogo Prefecture.
Climate warming during the mid-Cretaceous Period is believed to have enabled flowering plants to prosper in the Late Cretaceous Period, leading to a wider diversity of dinosaur species.
The two eggshell fossils from a later period in the reign of dinosaurs could provide clues on their evolution in coastal areas of East Asia and on changes in ecology.
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