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.” Dinosaurs were reptiles and most hatched from eggs. No dinosaurs could fly and none lived in the water. Plant-eating sauropods were the largest animals to ever walk on earth, but blue whales are more massive than any of the dinosaurs were! The largest dinosaurs were over 100 feet long and up to 50 feet tall (like Argentinosaurus, Seismosaurus, Ultrasauros, Brachiosaurus, and Supersaurus). The smallest dinosaurs, like Compsognathus, were about the size of a chicken.