Dinosaurs were the first to lay soft-shelled eggs, and some species evolved hard-shelled eggs, new Scientist reported.
American Museum of Natural History scholar Mark Norrell and his team found a batch of embryos in Mongolia believed to be proceratops. This dinosaur lived between 83 and 72 million years ago. The fossils were found “in a fetal state, all curled up,” with each embryo wrapped in a membrane, Norrell said.
The team also examined the remains of murosaurus embryos. The embryo of Ratosaurus, an early dinosaur that lived about 200 million years ago, was also coated with a thin film.
Jasper Weiman, a member of the research team at Yale University in the United States, found that the membranes surrounding the embryos contained degraded residues of egg proteins. Wieman then examined the eggs of 26 extinct and living animals and found that hard-shelled and soft-shelled eggs were made of different proteins, which leave traces behind when the eggs fossilized. Weyman analyzed egg samples from protoceratops and Ratosaurus and found that “both fit the characteristics of soft-shelled eggs.”
To find out whether the earliest dinosaur eggs were soft or hard, Matteo Fabry, also of Yale, built a database of eggs of 112 living and extinct reptiles and birds whose evolutionary relationships are known to science. It turns out that many early species, including lizards and dinosaurs, laid soft-shelled eggs.
The early dinosaurs eventually split into three main groups: sauropods, such as murosaurus; Ornithosaurs, such as protoceratops; Theropods, large meat-eating dinosaurs like Tyrannosaurus Rex, and modern birds. “All three branches independently evolved hard-shell eggs,” Fabry said.