In 1922, the first good dinosaur skeletons from Mongolia were discovered by an expedition from the American Museum of Natural History. The area soon became famous for its nests of dinosaur eggs, and the quality of preservation of its dinosaur skeletons. Russian-Mongolian, Polish- Mongolian, and numerous other expeditions have made the Upper Cretaceous beds of Mongolia one of the richest sources of dinosaurs. The paleoenvironments represented are diverse, and each has its own characteristic fauna. The Djadokhta Formation and its equivalents, for example, represent arid regions that produce many skeletons, but of relatively low diversity. Nevertheless, the conditions were favorable for the preservation of eggs, birds, mammals, lizards, and small dinosaurs. The somewhat younger Nemegt Formation was laid down under more favorable conditions, and has yielded more than 35 species of dinosaurs. Although it has been heavily prospected, new discoveries are constantly being made. Small theropod and bird skeletons are relatively abundant, but many animals continue to be known only from partial skeletons. A complete skeleton of the unusual theropod Ingenia was one of the prizes of last summer's fieldwork.

Over the last two decades, there has been steadily increasing interest in dinosaur footprints. In part this is tied in with the discovery of many new footprint sites in Asia, North America, and South America. More importantly, however, is the improved ability to extract information about the paleobiology of dinosaurs from the footprints and trackways.

Well-preserved footprints from the Nemegt Formation of Mongolia can be associated directly with skeletons of Tarbosaurus, Opisthocoelocaudia, and Saurolophus. These ichnites include the impressions of the skin on the bottoms of the feet and along the lower parts of the leg. Whereas the skeletons from the Nemegt localities show a preservational bias that favors the recovery of carnivores, the footprints clearly show that the ecosystem was dominated by herbivores. Although feet tend to be conservative in their anatomy, well-preserved footprints can sometimes reveal an unexpected diversity of forms.