Paleontologists have long thought that all dinosaurs laid hard-shelled eggs, much like crocodiles and birds (their descendants) do.
But a new analysis of fossil eggs discovered in the Gobi Desert throws cold water on that theory — and changes our understanding of dinosaur evolution.
“I’ve been excavating in Mongolia for 20 years now, and we find a lot of dinosaur eggs. But these сɩᴜtсһeѕ tell us something very different from what we knew before,” mагk Norell, lead author of the study and paleontologist from the American Museum of Natural History, told Business Insider.
But this discovery helped the study authors determine that the oldest dinosaurs laid soft-shelled eggs, and that hard-shelled eggs cropped up much later in the dinosaur fossil record than paleontologists previously thought.
“It was clearly a concentration of very, very small animals curled up in fetal positions, like you’d find inside an egg” Norell said. “It’d barely be four inches long if you ѕtгetсһed one oᴜt.”
The other eggs belonged to Mussaurus, a 20-foot, long-necked, herbivore that lived between 227 and 208.5 million years.
He and his colleagues discovered that nine of the Protoceratops embryos were surrounded by egg-shaped, black-and-white halos. Norell’s co-author, Jasemina Wiemann, used a special type of microscope to isolate the minerals left behind in those halos from the surrounding rock and chemically analyzed them.
“It was quite exciting to see that they looked exactly like soft-shelled snake or turtle eggs,” Wiemann told Business Insider.
Fabbri and his colleagues found that hard-shelled eggs had evolved at least three times in the dinosaur family tree: once in the Ornithopods, which included dᴜсk-billed dinosaurs; once in the giant Sauropods like Titanosaurs; and once in the Therapods (like T. rex) of the late Cretaceous period.
The study authors’ conclusion matches the hard-shelled eggs that have already been found in the fossil record — eggs belonging to ѕрeсіeѕ in the aforementioned dinosaur groups.
