How did the dinosaur eggs hatch?

Similar to modern birds and reptiles, dinosaur young cracked their way out of eggs when they were ready to enter the world. Also similar to these modern species, certain dinosaur species were apparently too small and weak to leave the nest after hatching. In most cases, the baby dinosaurs probably remained nest-bound for many weeks after they hatched, and had to be fed and tended by the adults. Scientists have deduced this from several nest sites that show the fragments of trampled egg shells and remains that look like regurgitated leaves and berries. Similar to the young of most species, dinosaur hatchlings were no doubt especially susceptible and vulnerable to attacks from predators that hunted around the nesting sites.

Paleontologists can often tell whether the young were independent once they hatched or needed parental care based on the state of the egg fossils found. Some babies may have stayed with their mothers for a long time before they were mature enough to forage for themselves (Big Stock Photo).

How can parental care traits of dinosaurs be extrapolated from living animals?

Of course, the parental care traits of dinosaurs cannot be directly observed because theyve been extinct for 65 million years. Therefore, paleontologists have had to resort to observing the closest living relatives of the dinosaurs: birds and crocodiles. They believe that these modern animals probably had many of the same traits, including construction of nests or mounds, nesting together in rookeries, guarding the nest by one or both of the parents, warning and recognition sounds made by the young, and family group cohesiveness during the hatchling stage. In fact, many of these traits have been confirmed by recent fossil findings.

Are there any examples of the dinosaur parenting care methods?

Yes, there are some examples of parental care methods that scientists have painstakingly pieced together, mostly from known fossil nesting sites around the world. The first example is the Orodromeus, an ornithopod that lived in Montana during the Cretaceous. This dinosaur laid its eggs in spirals, with the large ends up and tilted towards the center; the average clutch included 12 eggs. The young hatched with well-developed limb bones and joints, suggesting they could walk almost immediately. This is supported by the low number of crushed eggs in the nest site, indicating the young left quickly. Fossil evidence shows the young stayed in groups, but it is not known for how long.

The Maiasaura were also ornithropods in Montana during the Cretaceous. These dinosaurs made nests in shallow holes that were spaced apart from the surrounding nests by about the length of an adult dinosaur. On average, there were 17 eggs per clutch. The fossil evidence to date suggests that the hatchlings had poorly formed limb joints, which meant the young had to stay in the nest for an extended period of time. This conclusion is supported by the numerous fossils of hatchlings found in the nests, along with trampled and crushed eggs. This means that the young Maiasaura needed a large amount of parental care and attention, with some estimates having the young staying in the nest for approximately eight to nine months.

Another Cretacious period dinosaur, the Oviraptor, was a theropod living in what is now Mongolia. One of the most exciting recent fossil finds is that of an Oviraptor in a nesting position, suggesting a brooding behavior similar to modern birds. In contrast to this nurturing attitude, the Coelophysis theropods of the Triassic period found in Arizona probably ate their young, as seen in many fossil remains.

Were Triceratops social animals?

Similar to todays creatures, not every dinosaur was a social animal. But scientists have discovered that Triceratops, which were once thought to be aloof, solitary, shy herbivores, may have actually liked being around others of their kind. The evidence for this was recently uncovered in southeastern Montana in Late Cretaceous rocks. Discovered in the 66-million-year-old rock were the bones of at least three juveniles (they were probably all together when a flood struck the area). Some scientists are not sure, but this behavior may have been for protection, and it may have been more common in juveniles than in adult Triceratops.

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