To paraphrase Samuel Butler's (1825-1902) famous epigram, 

"A dinosaur is only an egg's way of making another egg"

Roy Chapman Andrews made many important fossil discoveries during the American Museum of Natural History's expedition to the Gobi Desert in the early 1920s but, in terms of public excitement, none surpassed the dinosaur eggs he brought back. A celebrity auction in New York City immediately established the monetary value of a single egg at $5000. But the paleontological worth of dinosaur eggs is inestimably greater.

Dinosaur eggshell fragments are not common in the Cretaceous rocks of Alberta. Unless they occur with abundant fossil clams and snails, which buffer the calcite of the eggshells, these calcareous fragments tend to be dissolved. The discovery of eggs, embryos and nests in the Two Medicine Formation (Late Cretaceous, 75 million years old) at Devil's Coulee near the Milk River in southernmost Alberta by a Tyrrell Museum field crew headed by Phil Currie in 1987 started the study of dinosaur embryos in Canada. This site proved to be amazingly productive. It yielded eggs, many with embryos, some dinosaur hatchlings and nests -- one containing a clutch of 8 eggs -- in addition to 20,000 isolated eggshell fragments. The eggs are large -- nearly spherical and 20 cm diameter with a volume of nearly 4 litres. The large embryos almost entirely fill the eggs and the embryonic bones are sufficiently well preserved to identify the hadrosaur Hypacrosaurus. At least nine separate nests were located in this area; evidence that Hypacrosaurus nested communally. But the herbivorous dinosaur was not the only animal using this site. Distinctive eggshell microstructure indicates that birds nested here and, surprisingly, so did theropod dinosaurs.

During its growth from embryo to adult the weight of Hypacrosaurus increased by 16,000 times -- evidence that they were active warm-blooded animals with healthy appetites; definitely not sluggish creatures with slow physiologies.

Further reading:

Carpenter, K., Hirsch, K.F. and Horner, J.
1994:  Dinosaur Eggs and Babies. Cambridge University Press.