The Polish-Mongolian Paleontological Expeditions worked at Bayn Dzak, Bayn Shireh, Nemegt , Toogreeg and many other locations in Gobi. A large number of dinosaur skeletons were collected due to intensive and well organized field program. Many of dinosaurs found by the expeditions were eventually described as new taxa of small dome-headed dinosaurs ( Homalecephale and Prenocephale ) , a mysterious theropod ( Deinocheirus ) , a small agile birdlike theropod ( Avimimus ) , the ostrich-like dinosaur ( Gallimimus ) , and two large sauropods ( Nemegtosaurus and Opisthocoelicaudia ) .
Two unusual dinosaurs, called pachycephalosaurids, were unearthed from beds of the Nemegt Basin by the Polish-Mongolian Paleontological Expeditions. These two dinosaurs had characteristic by 8 to 10 cm thick bony cap of their skull. This strange adaptation has been interpreted as used by males to compete for females by holding head-ramming contests, as we can see in mountain sheep.