Geoscience Reference
In-Depth Information
CHAPTER
FIVE
Dinosaur Eggs
Evolutionary Time Capsules
Dinosaur eggs have been found on all continents except Antarctica.
Among the oldest are those associated with the tiny prosauropod
hatchlings of
Mussasaurus
from the late Triassic of South America.
The few known late Jurassic sites are restricted to North America,
Europe, and Tanzania. Eggs from the early Cretaceous are far more
abundant, but with the exception of one site from southern Australia,
all are restricted to the Northern Hemisphere. Although a large num-
ber of late Cretaceous sites yielding dinosaur eggs have been found
across North America, Europe, and Asia, relatively few have been dis-
covered in the Southern Hemisphere. Only South America and India
have provided evidence of dinosaur nesting sites in the southern
continents at the end of the Mesozoic, probably due to the limited
amount of paleontological exploration of the continents that occu-
pied the Southern Hemisphere at that time (including India).
An egg for an embryo is like a space suit for an astronaut. A
dinosaur egg has numerous special structures to nourish the embryo
growing inside and provide protection from the hostile environment
outside. The most obvious is the shell. A few reptiles, such as sea tur-
tles, some lizards, and snakes, lay flexible or soft-shelled eggs, but in
dinosaurs, as well as in most other reptiles, the shell is primarily
composed of hard mineral crystals called calcium carbonate—the
same basic material that makes up limestone and cement. These crys-
tals, which are arranged into distinctive structural units that fit
tightly together and occasionally interlock, form a hard shell that cre-
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