Nest and egg clutches of the dinosaur Troodon formosus and the evolution of avian reproductive traits

Living archosaurs (crocodilians and birds) share several reproductive features, including hard-shelled eggs1, parental care2,3, assembly-line oviducts4 and luteal morphology5. Nevertheless, crocodilians produce many small eggs that they ovulate, shell and deposit en masse, and incubate within sediments or vegetation mounds2,4,6, whereas birds produce fewer but larger eggs7, usually from a single ovary and oviduct3. Further, birds ovulate, shell...