Millions of years ago, long before humans were alive, dinosaurs were around. Dinosaurs were one of several kinds of prehistoric reptiles that lived during the Mesozoic Era, which means the age of reptiles.

There were lots of different kinds of dinosaurs that lived at different times. Their qualities included the following:

*Dinosaurs could walk on either two or four legs. Some dinosaurs could do both.

* Some were fast and some were slow.

* Some had horns, crests, spikes, or frills.

* Some had thick, bumpy skin, and some even had primitive feathers.

It is very difficult to figure out how the dinosaurs sounded, how they behaved, how they mated, what color they were, or even how to tell whether a fossil was male or female.