Birds are the closest living relatives of dinosaurs, which is why it was long assumed that dinosaur eggs developed similarly to avian embryos. But new research found that the incubation period for dinosaur embryos was approximately 3 to 6 months, which is closer to the development of reptile eggs. Researchers came to this conclusion after analyzing fossilized teeth from dinosaur embryos of different species. Their findings suggest that avian dinosaurs may have evolved for shorter incubation periods. Unfortunately, there are no avian dinosaur fossils in good enough condition to test this theory.
Gregory M. Erickson, Darla K. Zelenitsky, David Ian Kay, and Mark A. Norell
Original paper published in PNAS on January 2, 2017.