Digging the history of a particular creature is what scientists do for several years. Reports published in a specific Journal says that, about 90 million years ago, a giant turtle in what is now central China laid a clutch of tennis ball-size eggs with extremely thick eggshells. One egg never hatched, and it remained undisturbed for tens of millions of years, preserving the delicate bones of the embryonic turtle within it.
In 2018, a farmer discovered the egg and donated it to a university. Now, a new analysis of this egg and its rare embryo marks the first time that scientists have been able to identify the species of a dinosaur-age embryonic turtle.
The newfound fossil belongs to an extinct group of land-dwelling turtles known as the nanhsiungchelyids, according to a new study published in proceedings of the Royal Society B. This group grew to momentous sizes and walked the Earth alongside the dinosaurs during the Cretaceous, a period that spanned from 145 to 66 million years ago. The turtle that laid the fossil egg—which is among the largest known from this time—was exceptionally big and likely sported a shell about as long as an average person is tall, the team estimates. While these turtles’ unique terrestrial lifestyle, thick eggs, and underground nesting strategy may have served them well during the Cretaceous, it’s possible that these specialized turtles couldn’t adapt to the cooler “climatic and environmental changes following the end-Cretaceous mass extinction,” study co-researcher Darla Zelenitsky, an associate professor of paleobiology at the University of Calgary in Canada, told Live Science.
The farmer discovered the egg in Henan province, a region famous for the thousands of dinosaur eggs people have found there over the past 30 years, Zelenitsky said. But in comparison with dinosaur eggs, turtle eggs — especially those with preserved embryos — rarely fossilize because they’re so small and fragile, she said. The egg is known as Y. nanyangensis egg, however, persisted because it’s a tank of an egg.
The eggshell’s 0.07-inch thickness is also remarkable. To put that in perspective, that’s four times thicker than a Galápagos tortoise eggshell, and six times thicker than a chicken eggshell, which has an average thickness of 0.01 inch (0.3 mm). Larger eggs tend to be thicker, like the 0.08-inch-thick (2 mm) ostrich eggshell, but “this egg is much smaller than an ostrich egg,” which averages about 6 inches (15 cm) in length, Zelenitsky said.
The researchers used a micro-CT Scan to create virtual 3D images of the egg and its embryo. By comparing these images with a distantly related living turtle species, it appears that the embryo was nearly 85% developed, the researchers found.
Part of the eggshell is broken, Zelenitsky noted, so “maybe it tried to hatch,” but failed. Apparently, it wasn’t the only embryonic turtle that didn’t make it; two previously discovered thick-shelled egg clutches from Henan province that date to the Cretaceous, one with 30 eggs and another with 15 eggs, likely also belong to this turtle’s now-extinct family, known as Nanhsiungchelyid, the researchers said.
The study of the newfound egg is special for its virtual 3D analysis of the embryo, which helped lead to its species diagnosis, said Walter Joyce, a professor of paleontology at the University of Fribourg in Switzerland, who was not involved in the study. Furthermore, this study offers evidence that Nanhsiungchelyid turtles were “adapted to living in harsh, terrestrial environments, but laid their large, thick-shelled eggs in covered nests in moist soil,” Joyce told LiveScience in an email.