The following questions were answered by paleontologist Don Lessem, Tim Rowe, and Bill Hammer.
Dinosaurs are a group of animals descended from reptiles and the ancestors of birds.
They were different from their reptile ancestors in that they have an S shaped neck and feet held directly beneath their bodies, and several other features. They lived on land, grew both big and small, and died out 65 million years ago. Pterodactyls and other flying reptiles are pterosaurs, not dinosaurs, since dinosaurs didn't fly. But pterodactyls did live in dinosaur time. There were probably thousands of kinds of dinosaurs, but we haven't found most of them yet.