New research suggests that dinosaur eggs were more similar to reptiles rather than their descendants, birds.Scientists have long believed that dinosaur egg incubation periods would be similar to that of birds, roughly between 11 to 85 days. This would be proportional to the size of the eggs (the larger an egg, the slower the incubation period). However, research from the University of Calgary, Florida State University and the American Museum of Natural History suggests that this wasn't the case at all.
Dinosaur incubation periods directly determined from growth-line counts in embryonic teeth show reptilian-grade development
Little is known regarding nonavian dinosaur embryology. Embryological period relates to myriad aspects of development, life history, and evolution. In reptiles incubation is slow, whereas in birds it is remarkably rapid. Because birds are living dinosaurs, rapid incubation has been assumed for all dinosaurs. We discovered daily forming growth lines in teeth of embryonic nonavian dinosaurs revealing incubation times. These lines show slow reptilian-grade development spanning months. The rapid avian condition likely evolved within birds prior to the Cretaceous–Paleogene (K–Pg) mass extinction event.