Montshire Minute: Dinosaur Eggs

Originally aired during the week of September 1, 2003

Monday

There is lots of disagreement on how dinosaurs lived, partly because we have little more than fossil remains to work from. Most scientists agree that dinosaurs were "reptile-like." That is, they had dry, scaly skin, and eggs that were fertilized inside the female's body. Imagine how big dinosaur eggs must have been. I mean, these were the largest animals to walk on land! But eggs cannot be infinitely large. As eggs get bigger, their shells must get thicker - they must be strong enough to protect the embryo and fluids inside. The eggshell must also be porous enough to allow the exchange of oxygen and carbon dioxide. This transfer becomes more difficult the thicker the eggshell becomes. Thicker shells might have also made it more difficult for the hatching dinosaur to break through. This is why very large animals like dinosaurs had smaller eggs than one might expect for their size.

Tuesday

Dinosaur eggs and embryos often hold clues that help scientists trace dinosaur ancestry and piece together the lives of dinosaurs. But sometimes, the fossil evidence produces more questions than answers! English scientist Terry Manning figured out a way to pick apart fossils of embryonic dinosaurs. Using a microscope and a series of washes with acetic acid, he isolated bones, teeth, and claws of an embryonic dinosaur. One embryo had teeth similar to plant eating sauropods, the big, long-necked dinosaurs. Other teeth resembled those of ornithopods, a smaller plant eater. So how to classify this dinosaur called the therizinosaur? Perhaps that's a question for future paleontologists. Meanwhile, there are plenty of other dinosaur mysteries to investigate in our new exhibit Hatching the Past, opening on September 15!

Wednesday

Paleontology is the study of long extinct life forms. But the field is changing all the time, as new discoveries are evaluated. One of the most surprising findings is evidence suggesting that some dinosaurs lived in organized groups and actually tended to their young. Dinosaur eggs and nests had been found in Mongolia in the 1920's, but then it was assumed that, like most modern reptiles, dinosaurs let their young fend for themselves after hatching. In the late 1970s dinosaur researchers uncovered many nest sites in North America. Clusters of nests suggested dinosaurs nested in colonies, much like some bird species do today. Other nests also contained skeletons of juvenile dinosaurs. Based on seeds, berries, and other plant materials found at nest sites, researchers believe adults tended their young until they could forage for themselves.

Thursday

Researchers believe that some dinosaurs lived in large colonies. In some digsites, paleontologists have discovered several layers of nests, indicating that dinosaurs may have returned to the nest site year after year to breed. Unlike birds, reptiles don't sit on their eggs to hatch them. But female crocodiles are known to guard their nest, carefully covering the eggs with vegetation to keep them warm. Adult dinosaurs may have used vegetation to protect the eggs and encourage incubation. How do we know what dinosaurs laid which eggs? One way is to study hatchlings found in nests or by finding adult skeletons in nests with eggs. Groups of dinosaurs can be classified by the characteristics of eggs--their size, shape, thickness, and texture--and the microscopic structure of eggshells. At the Montshire Museum's new visiting exhibit Hatching the Past, you'll see over 50 dinosaur fossils. The exhibit opens September 15!

Friday

Researchers believe that many species of dinosaurs must have migrated to better feeding grounds, since trying to keep up with the nutritional needs of so many baby dinosaurs would have wiped out vegetation surrounding a nesting site. The hatchlings may have stayed under their parents' watchful eye through a migration period. Like many modern animals, they may have returned to their nesting site to raise their own families the following year. The lure of tender baby dinosaurs would have been attractive to predators, and we can imagine that many hungry carnivores lurked around nesting areas. While the babies were protected by their parents, the adult dinosaur still had to forage for food, leaving the young unprotected from time to time. By examining fossilized teeth of hatchlings, scientists believe that some dinosaur parents pre-chewed or digested food for their offspring.