Pliocene Epoch, second division of the Neogene Period of the Cenozoic era on the geologic time scale (see Geology), spanning an interval from about 5.3 million to 1.8 million years ago. Like the Miocene, which preceded it, the Pliocene was named and defined by the British geologist Sir Charles Lyell on the basis of the percentage of modern species of shellfish found in the fossil record. In western North America, subduction of the Pacific tectonic plate margin helped elevate the Sierra Nevada and the volcanic Cascade Range. In Europe, the Alps continued to rise as tectonic plate motion buckled the crust across a wide swath of that continent (see Plate Tectonics). The climate became cooler and drier with the approach of the Ice Ages of the Pleistocene Epoch. Mammals had long since established themselves as the dominant terrestrial life form, and the rapid evolution of one group, the primates, produced species considered direct ancestors of Homo sapiens.