In the early 1980s, paleontologists Jeff Eaton and Rich Cifelli started digging for fossils in one of the most inaccessible regions of the United States: the Kaiparowits Plateau of southern Utah. They were looking not for dinosaurs, but for ancestral mammals. Mammals almost litter the fossil record after dinosaurs became extinct 65 million years ago, but they were rare before then. Eaton and Cifelli ventured onto the Kaiparowits to comb its rocks for mammals’ tiny teeth and bones.
Not only did these two scientists find fossil mammals, they uncovered one of the most complete sequences of vertebrate fossils anywhere in the world from the time when dinosaurs still ruled. What Eaton and Cifelli discovered in Utah showed that life on land was unexpectedly becoming more diverse at a time when life in the oceans was being decimated by chemical changes.