Just like how humans and animals in different parts of the world today have different characteristics, the dinosaurs of millions of years ago also had their own unique habits and physical traits. For example, the dinosaurs in Mongolia during the Late Cretaceous period were less advanced than the ones living in North America.

The tyrannosaurids that lived in Asia were more primitive and smaller than those that roamed North America, and the only armored dinosaurs that lived in Asia were ankylosaurids such as Talarurus and Tarchia. Some dinosaurs, such as the segnosaurs, were found only in China and Mongolia. Examples of this group are the Erlikosaurus, Therizinosaurus and Segnosaurus. Certain small predators were more abundant in Asia, and ostrich-like ornithomimids were rare in Mongolia [source: Benton]. Paleontologists have found specimens from all of these species and more, which have helped them understand both past and modern life in the Gobi region [source: AMNH].

One Mongolian dinosaur, the Elmisaurus, was so unique that is was classified in its own family. The Elmisaurus, a small dinosaur 6 to 10 feet (1.8 to 3 meters) long, was originally discovered in Mongolia in the 1960s, as part of the joint Polish-Mongolian paleontological expeditions. Its name is derived from "elmyi," the Mongolian word for beautiful.

In 1981, Polish paleontologist Halszka Osmólska designated the Elmisauridae as a new family with just one member. It received this distinction because of its unique foot bones, which paleontologists had never seen before. Elmisaurus is also one of the few Late Cretaceous animals that had both North American and Asian species. The Chirostenotes pergracilis has been described as the North American cousin to the Elmisaurus, as the two creatures had very similar foot bones [source: Osmólska]. It's also believed that another North American dinosaur, the Ornithomimus elegans, could be placed in the Elmisauridae family.