Did all dinosaurs lay eggs?

As far as paleontologists can determine, all dinosaurs reproduced by laying eggs. The first fossilized dinosaur eggs were found in France in 1869, but not everyone agreed the eggs were from dinosaurs. Although it may seem somewhat obvious to us now, it took time before scientists agreed that dinosaurs nested and laid eggs. The proof was found in the 1920s in the Gobi Desert, where nests and eggs of a group of Protoceratops were found. Since that time, over 200 sites with fossil eggs of various dinosaurs have been found all over the world, including in the United States, France, Mongolia, China, Argentina, and India.

It should also be noted, though, that there are some modern reptiles that do not lay eggs outside their bodies; rather, their eggs remain inside them, where they hatch and then emerge as live young (this is called being ovovivaporous). Some scientists suggest that this is a result of adapting to colder climates. And although the idea is highly debated (and no real physical evidence has been found), some scientists speculate that polar dinosaurs may have reproduced in this way.

Have other clutches of dinosaur eggs been discovered?

Yes, there are hundreds of sites around the world that have large clutches of dinosaur eggs. For example, in a remote area of Argentina, in northwest Patagonia (Auca Mahuida), the concentration of eggs was so rich that, in an area of roughly 300 feet by 600 feet (91 meters by 183 meters), scientists counted about 195 clusters of eggs.

All dinosaurs laid eggs, making a variety of kinds of nests. Paleontologists have discovered many eggs and nesting sites in recent years, some including the fossils of not only eggshells but also hatchlings and even the mothers remains (Big Stock Photo).

What do dinosaur eggs look like?

Scientists have collected fossil dinosaur eggs, sometimes finding more than a dozen in a nest-like area. The fossilized eggs are usually the color of the rock in which they are found. Similar to fossil dinosaur bones, their structures have been fossilized and replaced by minerals over time.

Although the eggs are fossilized, scientists have discovered that dinosaur eggs probably looked similar to those of modern birds, reptiles, and some primitive mammals. Most of the eggs were rounded or elongated, with hard shells. They contained an amnion, a membrane that kept the egg moist, a kind of private pond for the young animal growing in the egg. The eggs appeared to be similar in other ways, too. The surface of the shell allowed for the exchange of gases necessary for the young to survive (many of the fossilized eggs exhibit a mottled surface that indicates the shell pores), and the young would crack their way out of an egg when they were ready to enter the world.

No one really knows whether the majority of eggs laid by the dinosaurs were soft-, flexible-, or hard-shelled. The eggshell would have to have been relatively strong to support the weight of a brooding parent, or the overburden of nesting material, while still allowing for the exchange of necessary gases. Hard-shelled eggs had the best chance of fossilizing, so most shells that we find today may not truly represent all the eggs that dinosaurs laid, but just the hardest ones that survived.

Where were the first clutch of dinosaur eggs discovered?

The first known clutch of dinosaur eggs were found by American naturalist Roy Chapman Andrews (1884-1960) in 1922 in the Gobi Desert, south of the Altai Mountains. The eggs were found in one of the most prolific fossil beds in the area, a sedimentary layer known as the Nemget formation, which is also known for the more than 100 fossil skeletons of the small horned dinosaur Protoceratops.

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