Dinosaur Eggs

Did All Dinosaurs Lay Eggs? Exploring the Reproduction Methods of Dinosaurs

When the first fossilized dinosaur eggshell fragments were discovered and described around 1860, most people—including most scientists—had no idea what dinosaurs were, let alone how dinosaurs were born. It wasn’t until 1920 that scientists first described dinosaur eggshells as dinosaur eggshells.

In the years since then, chance finds of eggs and eggshells have become one of the best windows into how tiny dinosaurs burst onto the world many millions of years ago.

Did dinosaurs lay eggs?

Paleontologists tend to believe that every single extinct dinosaur emerged from an externally laid egg, whether it was a triceratops, a tyrannosaurus, a stegosaurus, or some other type of dinosaur. In fact, although there is no definite evidence in the fossil record that any of these animals produced live offspring, there are abundant indications that they laid eggs filled with embryos.

So here’s all the dirt paleontologists have found about dinosaur eggs based on their fossils.

Did dinosaurs lay eggs individually?

Today’s paleontologists tend to agree that different types of dinosaurs laid different amounts of eggs. While some species produce about 1 to 5 per sitting, others produce about 15 to 20. Paleontologists have even found a type of dinosauron psittacosauruss, which lay about 35 eggs at a time.

The laying of large brood nests was a common practice among dinosaurs, and a profitable one at that. Since carnivorous dinosaurs had a habit of devouring almost any eggs they could find, laying many eggs at once became one of the best ways for female dinosaurs to ensure that at least one hatched successfully.

Read more: How did dinosaurs mate?

Types of dinosaur eggs

Even despite the egg-eating habits of carnivorous dinosaurs, the prevalence of such large batches of offspring suggests, in theory, that the world is full of intact dinosaur egg fossils. But paleontologists find these specimens only occasionally in practice, as they tend to break during the storage process.

As a result, far more common than intact dinosaur eggs are the broken pieces of dinosaur eggshells that are scattered throughout the sediment of paleontological sites around the world.

Read more: Why an extraordinary collection of dinosaur embryos remains locked away from science

The structure of dinosaur eggs

Whether intact or in fragments, scientists struggle to determine the identity of dinosaur eggs when they are not found in close proximity to their fossilized parents. (Even then, identification can still present problems, with parents of potential offspring sometimes being mistaken for foraging predators.)

That being said, the basic features of an egg can provide paleontologists with broad clues as to its origin, with the features of theropod and sauropod eggs often being at opposite ends of the structural and aesthetic spectrum.

How big were dinosaur eggs?

Take the size of eggs for example. Scientists say that adult dinosaurs laid eggs in a wide variety of sizes, with theropod eggs being both smaller and larger than sauropod eggs.

Oddly enough, although it might seem reasonable to assume that the largest dinosaurs—the tall, leaf-loving sauropods—laid the largest eggs, there isn’t always a clear correlation between the size of the dinosaurs and the size of their eggs. Instead, the theropods of the Oogeny, Himeolite and Macroelongatoolithuslay the smallest and largest dinosaur eggs ever found, which are about 2 and 24 inches long.

The shape of dinosaur eggs

And that’s not the only thing that distinguishes different future dinosaurs. In fact, scientists say that adult dinos also laid eggs in a wide variety of shapes, with theropods having elongated eggs and sauropods having spherical ones. According to these scientists, this difference is probably due to the different terrains that theropods and sauropods inhabited.

The color of dinosaur eggs

Size and shape are not even the extent of the differences between these fossil specimens. in 2018 analysis from Nature found a range of different colors and coloring patterns in the eggshells of an assortment of different dinosaurs. And while theropod eggs are usually bright blue and green, those of sauropods are brown, beige and white.

According to the authors of this analysis, these colors did much more than distinguish the offspring of theropods, sauropods, and several other dinosaur species. They also protected the offspring from predators, with some shades acting as a form of camouflage.

The texture of dinosaur eggs

There’s also the matter of texture.

Paleontologists have traditionally thought that dinosaurs produced hard-shelled spongy eggs, and it’s no wonder why. For years, the only eggshells they had found were porous and hard. But studies have since shown that the texture of these shells varies greatly depending on the type of dinosaur that produced them.

Although dinosaur eggs are porous, allowing the transfer of oxygen and other supporting substances across the surface of the shell, these pores show considerable diversity in terms of their shape, size, and density. In fact, research of 2015 says that preserved theropod eggshells are much more porous than those of sauropods, again due to differences between their environments.

Even more confusing is the malleability of dinosaur eggs. According to analysis as of 2020, plenty of dinosaurs actually laid soft-shelled leathery eggs, despite their rarity in the fossil record. And although these soft-shelled specimens are less likely to have survived the preservation process, the analysis has gone so far as to suggest that they were standard throughout early dinosaur evolution.

Read more: This is what dinosaurs really looked like

Structure Signals Behavior

Overall, scientists suggest that these traits hint at how dinosaurs treated their offspring. For example, the roll-resistant, elongated shapes, camouflage colors, and semiporous shells of theropod eggs suggest that these dinosaurs organized their offspring in open nests. But the absence of these traits among sauropod eggs suggests that they instead arranged their offspring in enclosed cavities.

Also, while the hard-shell structure of the eggs of some species could support the weight of a parent, the soft-shell structure of others would not, preventing those parents from engaging in a range of brooding behaviors.

Read more: What species today are descendants of dinosaurs?

Protective parents?

Dinosaur parents were just as different as dinosaur babies. Different dinosaurs devote different amounts of time and attention to their eggs throughout the incubation period, which takes from three to six months.

Some species tirelessly care for their eggs. Take, for example, oviraptors. In addition to finding an abundance of these theropods near their nests, paleontologists have also found their fossils on their nests. Positioned in seemingly resilient sitting positions, these oviraptors braved the threats of predation and starvation to shelter their offspring, making them the picture of protective parenthood.

At the other extreme, some species appear to abandon their eggs immediately after they are laid. Fossils reveal that several species of sauropods, including Apatosaurus, buried their babies rather than torture them, letting them emerge from their shells on their own.

Read more: A dinosaur hatchery with 92 nests and over 250 eggs found in India

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