Dinosaur eggshells unearthed in Japan

An area of 20 square metres is slightly smaller than a tennis court. That is more than enough room for a game-changing discovery that sheds new light, and opens up more questions, about the diversity of dinosaurs in Cretaceous-era Japan.

Fossilized fragments of a new type of dinosaur egg have been found in Tanba, Hyogo Prefecture. 
The egg is characterized by a unique branch-like pattern on the surface. 
The scale is graduated in millimeters [Credit: Takeshi Ito]

An unprecedented discovery of fossil eggshell fragments in Japan’s Hyogo prefecture shows that the region’s dinosaur population was more diverse than researchers — and the world — had ever known. Kohei Tanaka, a doctoral student in the Faculty of Science, analyzed 90 fossil eggshell fragments recently unearthed from a site in the Kamitaki area in Tamba City. The results of his detailed analysis revealed something surprising: five different types of dinosaurs inhabited the region some 110 million years ago, during the early part of the Cretaceous period.

A recently published paper in the Cretaceous Research journal reveals that the eggs belonged to a variety of dinosaurs, including those of meat-eating dinosaurs (the evolutionary predecessors of birds) as well as plant-eaters. The paper is jointly authored by Tanaka, Darla Zelenitsky, and Christopher DeBuhr from the University of Calgary, and partners from the University of Hyogo, Museum of Nature and Human Activities, Hyogo, and Alberta’s Royal Tyrrell Museum of Palaeontology.

Dinosaur fossil finds rare in Japan

Dinosaur bones are extremely rare in Japan; dinosaur eggshells even moreso. “It is difficult to find fossil eggshell fragments in Japan because the rock is so hard and needs to be broken apart manually, whereas in Alberta, the sediment is generally soft and can be screened for pieces of eggshell,” explains Zelentisky, Tanaka’s PhD supervisor and professor of geoscience. The layers of dinosaur-age rock are limited in Japan, and volcanic and underground geological activities have hardened and squeezed the rock layers, making fossils more difficult to find.

Artist reconstruction of the Tamba City site, where fossil eggshell fragments
 from five species of dinosaurs have been uncovered 
[Credit: Masato Hattori]

With Japan’s vegetation-covered landscape, dinosaur fossils are even harder to come by, because most of the rocks containing them remain hidden. Discoveries have increased rapidly in recent years; however, only 20 dinosaur-bearing sites have been found since 1978 in the entire country. The riverside Kamitaki site, where fossilized bones of frogs, dinosaurs, and reptiles have also been found, is now believed to be the first dinosaur nesting site found on the Japanese islands.

After bones discovered by an amateur fossil hunter in 2006 alerted researchers to the presence of potential fossils at the site, its grounds have proven to hold important new information about the region’s dinosaur-age inhabitants. “[These eggshell fragments] can tell us a lot about the evolution, reproduction, and biology of dinosaurs in this region,” Tanaka explains.

Eggshells reveal five different types of dinosaurs

Since the initial site discovery, volunteers and researchers from the University of Hyogo and Hyogo’s Museum of Nature and Human Activities have been working to extract fossils from the rocky ground. Tanaka completed most of the examination of the eggshells through microscopic analysis at the University of Calgary, and also travelled to Hyogo to initially examine the specimens.

By analyzing the eggshells — whose microstructure can help identify the type of dinosaur they belonged to — the team was able to identify the five different types of dinosaur eggs from the discovered fragments.

The Kamitaki site fossils are opening up both questions and new possibilities for future research on dinosaurs in Asia. “This discovery will make people look more closely for eggshells,” says Zelenitsky. “They’d be easy to miss because they’re so small. They could exist at other sites, but maybe people didn’t see them or recognize them.” Adds Tanaka, “The quality of the specimens is very good. We’re hoping to find more dinosaur eggshells or complete eggs and nests [at that site] in the future.”

Author: Erin Guiltenane | Source: University of Calgary [July 03, 2015]