Knowing what an animal eats is extremely important, since eating takes up so much of an animal's time. Fossilized feces, called coprolites, contain bits of the last food a dinosaur was eating. A surprising number of coprolites have been found. In a few cases they were discovered inside the dinosaur's skeleton, but in most cases there is no way of knowing for certain which coprolites belong to which dinosaur. Carnivore dung is more common than plant-eater, probably because of the high proportion of bone in their food.
Other kinds of dinosaur fossils give scientists additional insights. A single animal leaves millions of footprints in its lifetime. If any of these footprints are preserved, it can give lots of information about the animal's lifestyle. Footprints were the first clue that many dinosaurs lived in large groups. They also show whether an animal walked on two legs or four, and can be used to calculate how fast it moved.
Sets of footprints, called trackways, tell us if an animal was traveling alone, in a pair, or in a group. Sometimes we find different sizes of the same footprint, telling us that some dinosaurs raised their young. Some trackways have been traced for hundreds of miles!
It had always been assumed that dinosaurs laid eggs, as all large reptiles do. In the 1920's, an expedition into the Gobi Desert uncovered several nests and skeletons of the Protoceratops. Most dinosaur eggs have been found in nests. These were usually holes in the ground without much preparation.
The total number of eggs in a single nest is usually about 22. The eggs themselves came in all shapes and sizes. Some were circular and the size of a tennis ball, others were up to 21 inches (53 cm) in length.
For the dinosaur-enthusiast, a few gift ideas...
National Geographic Dinosaurs, by Paul Barrett has lots of great information on dinosaur behavior, and includes some interesting parts on marine life. The Illustrated Encyclopedia of Dinosaurs, by Dougal Dixon is the book you wanted as a kid that had every kind of dinosaur in it. It has the dossier on 355 varieties. Both have awesome artwork, naturally!
If you happen to be shopping for a child under 12 who likes dinosaurs, check out Encyclopedia Prehistorica Dinosaurs, by Eric Sabuda and Matthew Reinhart. It's a pop-up, and it's cool as hell!
My previous posts on dinosaurs are here.