100-million-year-old turtle-embryo fossil found in Central China

A fossilized egg from an extinct prehistoric giant turtle and with an embryo still inside has been discovered in Central China's Henan province.

The fossil, dating back to about 100 million years ago, during the Cretaceous period, is a complete egg containing embryonic remains.

According to researcher Han Fenglu, from the China University of Geosciences (Wuhan), who first discovered the ancient egg during a field trip in Henan in 2018, it is rare to successfully link up a turtle egg fossil with a specific genus.

Based on 3D reconstruction, with the help of high-precision micro-CT scanning, the researchers have confirmed that the huge and unusually thick-shelled egg was from the Nanhsiungchelyidae, an extinct group of large terrestrial turtles. The turtle that laid the egg was likely up to 1.6 meters long.

The egg shell was nearly 2 minimeters thick, making it among the world's largest and thickest-shelled Mesozoic turtle eggs so far discovered. Researchers are still investigating the reason for the thick shell, but they say it was probably an adaptation to an unusually extreme environment at that time.

"We have found a structure that looks suspiciously like bone in the broken part of the eggshell," said Han. "It is likely a baby turtle close to breaking out of its shell."

Turtles originated in the late Triassic period and gradually evolved into reptiles over a period of more than 200 million years.

The results of the research into the fossilized egg have been published online in the journal Proceedings of the Royal Society B: Biological Sciences.