Millions of years ago, long before there were any people, there were dinosaurs. Dinosaurs were one of several kinds of prehistoric reptiles that lived during the Mesozoic Era, the "Age of Reptiles".

The largest dinosaurs were over 100 feet (30 metres) long and up to 50 feet (15 metres) tall (such as Argentinosaurus, Seismosaurus, Ultrsauros, Brachiosaurus and Supersaurus). The smallest dinosaurs, like Compsognathus, were about the size of a chicken.