Long ago, strange beasts roamed the world. Some grew as big as a barn, others were smaller than a hen. Some walked on four legs, others on two. Some were fierce hunters, others were peaceful plant-eaters. These backboned land animals are called dinosaurs. Dinosaur means "terrible lizard," and like lizards, dinosaurs were reptiles. But instead of sprawling, they walked upright, and some dinosaurs had feathers rather than scaly skin. In chilly air, instead of dozing like a lizard, some dinosaurs could stay active by generating their own body heat. The dinosaurs ruled Earth for 160 million years — flourishing on land more successfully than any other group of backboned animals. Then 65 million years ago, they mysteriously died out, except for one group — the dinosaurs that we call birds.
