Standing in a farmer's home in China's Henan Province in the summer of 2018, paleontologists Fenglu Han and Haishui Jiang peered down into a box of rounded lumps of rock. The farmer had collected the trove near his home in Neixiang County, which is renowned for its dinosaur eggs. One stony orb in particular caught the scientists' eyes. About the size and shape of a billiard ball, the fossil was unlike any dinosaur egg they'd seen before.

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