 The reconstruction of ancient marine and terrestrial environments, biostratigraphy, paleoecology, and mass extinctions are some of his interests.In addition to dinosaurs, he has described and named many fossil mollusks and fish.His researches in the middle Cretaceous of Utah indicate that the origins of Alaska and the first great Asian-North American faunal interchange occurred about 100 million years ago, which his numerous trips to China and Mongolia have substantiated.