Paleontologists from the American Museum of Natural History and the Mongolian Academy of Sciences have worked at Ukhaa Tolgod, in the Gobi Desert of Mongolia, since they discovered the site in 1993. Although its cliffs and scenery are not as spectacular as many other fossil sites in Mongolia, Ukhaa Tolgod has yielded more skulls of dinosaurs, mammals, and lizards than any other Cretaceous fossil locality ever discovered. This specimen (above) of an adult Oviraptor sitting on a nest of eggs is the first unequivocal evidence of brooding behavior in non-avian dinosaurs. Dinosaur embryos, one of which is shown above, are extraordinarily rare. Identical eggs found by Museum scientists in 1923 at the Flaming Cliffs, also in the Gobi Desert, were identified as the plant-eater Protoceratops. This specimen shows that they actually belonged to Oviraptor. Although mammals were contemporaries of dinosaurs, their remains are very rare and fragmentary. Scientists from the American Museum of Natural History and the Mongolian Academy of Sciences have collected more than 240 mammal skulls like the one shown here from Ukhaa Tolgod. In fact, this extraordinary locality has produced more mammal skulls than all other Cretaceous localities in the world combined.

The Gobi Desert is a half-million square miles of arid wilderness and high mountains -- five times the size of Wyoming -- that is a Mecca for paleontologists. This map shows the routes and localities visited by American Museum of Natural History and Mongolian Academy of Sciences researchers over the last six years.