Oldest dinosaur eggs and the evolution of dinosaur reproduction

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A new study on the oldest known dinosaur eggs has revealed new information on the evolution of dinosaur reproduction. The study looked at 195 million year old early sauropod eggs from sites in Argentina, China, and South America. The study attempted to explain why, despite the appearance of reptile and mammal precursors around 316 million years ago, fossilized eggs do not appear in the fossil record until 120 million years later. The eggs in this study had thinner and more brittle shells than similar-sized bird eggs. The study observed various factors, such as shell thickness and pore distribution, in an attempt to show why dinosaur eggs developed hard shells. The study suggests that hard-shelled eggs evolved early on in dinosaur evolution and that increased shell thickness occurred independently in several groups, with other reptile groups developing hard-shelled eggs a few million years later. It is believed that dinosaurs evolved eggs with harder shells in an attempt to defend the developing embryos from predation, likely by burrowing invertebrates. The researchers have raised new questions for future investigation, such as why dinosaurs and birds never developed viviparity when several other reptile groups, such as marine reptiles, did. Here is a link to the paper published about this study.


Paper (open access!): https://www.nature.com/articles/s41598-019-40604-8