The earliest amniotic eggs contained large amounts of yolk, says James R. Stewart, a reproductive physiologist at East Tennessee State University. “You still see that in birds, crocodilians, and ...

Some people argue that the egg came first. Those people believe that the egg was "laid by dinosaur ancestors" of the chicken.

Having made the link between hard-shelled eggs and life on land, scientists and reporters thought they had laid the issue to rest, so to speak: The hard-shelled egg appeared on the scene, allowing ...