In their day, dinosaurs ruled the Earth — at least what was covered by land. Their fossilized remains have been found on every continent. During much of the dinosaurs' reign, the current continents comprised a single, giant landmass called Pangea. Although knowledge of global dinosaur diversity remains very sketchy, in North America, where dinosaurs occurred from Alaska to Mexico and from coast to coast, more kinds may have roamed than anywhere else. They left behind a wealth of fossils, most of which probably still await paleontologists.

The United States can already claim more different kinds of dinosaurs than any other country or continent. More than 75 dinosaur genera, from Late Triassic types (which lived about 220 million years ago) to some of the last surviving Cretaceous creatures (which died off with the giant asteroid extinction 65 million years ago) have been recognized in the fossil record of the United States. And new additions keep appearing. In the past few years, Utah, always a rich source of the magnificent beasts, yielded limb bones and the lethal claw of the intimidating carnivore Utahraptor. From Oklahoma came the massive back bones of Sauroposeidon. With a 40-foot-long upright neck, Sauroposeidon surely was the tallest dinosaur that ever lived. And the latest finds from the Southwest's Zuni Basin introduced two more American dinosaurs.

Mongolia, China and England have each contributed dozens of different dinosaurs, but Canada rounds out the list of top-five dinosaur-producing nations. So for sheer numbers, North America rules as the global dinosaur hot spot.

One reason is that people have been looking hard for fossils in North America for about 150 years. The continent's first dinosaur skeleton of any size came from Haddonfield, N.J. There, in 1858, paleontologist Joseph Leidy discovered and later described the duck-billed dinosaur Hadrosaurus foulkii. Ten years later at the Academy of Natural Sciences in Philadelphia, Hadrosaurus became the world's first dinosaur skeleton put on public display. It was an appropriate initial discovery, as hadrosaurs lived as far west as New Mexico and north into Canada and Alaska. Duck-bills such as Edmontosaurus and Maiasaura include some of the most abundant dinosaurs anywhere.