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Scientists must use indirect evidence to determine whether extinct dinosaurs cared for their young. A. Because baby dinosaur bones and eggs were very delicate, there are relatively few preserved as fossils, so little is known about dinosaur young. B. Fossils from sites like Egg Mountain indicate that dinosaurs built nests, and perhaps that they incubated their eggs and fed their hatchlings. C. Fossil evidence such as the spacing of nests may indicate advanced parental care but can have different interpretations. D. Tightly packed Oviraplor rookeries indicate that dinosaurs may have tended to nest in large colonies in order to better protect both eggs and hatchlings. E. Discovery of hadrosaur bones of different sizes in the same nest may indicate that, in some species, older siblings took care of younger ones. F. The strongest evidence comes from extinct dinosaurs' nearest living relatives, birds and crocodiles, who do engage in many forms of parental care.