This was a period of great success for dinosaurs, with many new types appearing and diversifying. The duck bills, Ankylosauridae, and horned dinosaurs experienced success in Asiamerica (Western North America and eastern Asia).Tyrannosaurs dominated the large predator niche in North America.They were also present in Asia, although were usually smaller and more primitive than the North American varieties. Pachycephalosaurs were also present in both North America and Asia. Dromaeosaurs shared the same geographical distribution, and are well documented in both Mongolia and Western North America. By contrast therizinosaurs (known previously as segnosaurs) appear to have been living solely in Asia. Gondwana held a very different dinosaurian fauna, with most predators being abelisaurs and carcharodontosaurs; andtitanosaurs being among the dominant herbivores.