When did dinosaurs first appear?

The dinosaurs didn't suddenly "appear" on the earth. Animals evolved over millions of years to the point where they took the forms we are familiar with now as dinosaurs. The fossil record is clear in this. Smaller, less sophisticated creatures gave way to larger and more complex critters. Some 230 million years ago is the general time that paleontologists consider the dinosaur first appeared. Things rolled along until about 65 million years ago when the lights went out for the dinosaurs.

A link to the Wikipedia article on the dinosaur is provided.