indicating a diet of tough plant material, including tubers, nuts, and seeds—and possibly large quantities of grasses and sedges. Conversely, the Leakeys' 1960s finds presented different characteristics. The skull lacked a sagittal crest and the braincase was much more rounded, suggesting it was not australopithecine. The larger braincase suggested a larger brain capacity than that of Australopithecus boisei. These important differences indicated a different species, which eventually was named Homo habilis. Its larger brain capacity and decreased teeth size pointed to Homo as the probable toolmaker. The oldest tools at Olduvai, found at the lowest layer and classified as Oldowan, consist of pebbles chipped on one edge. Above this layer, and later in time, are the true hand-axe industries, the Chellean and the Acheulean. Higher still (and later still) are located Levallois artifacts, and finally the Stillbay implements. Oldowan tools in general are called "pebble tools" because the blanks chosen by the stone knapper already resembled, in pebble form, the final product.<ref>Napier, John. 1960. "Fossil Hand Bones from Olduvai Gorge." in Nature", December 17th edition.</ref> Mary Leakey classified the Oldowan tools according to usage; she developed Oldowan A, B, and C categories, linking them to Modes 1, 2, and 3 assemblages classified according to mode of manufacture. Her work remains a foundation for assessing local, regional, and continental changes in stone tool-making during the early Pleistocene, and aids in assessing which hominins were responsible for the several changes in stone tool technology over time. It is not known for sure which hominin species was first to create Oldowan tools. The emergence of tool culture has also been associated with the pre-Homo species Australopithecus garhi, and its flourishing is associated with the early species Homo habilis and Homo ergaster. Beginning 1.7 million years ago, early Homo erectus apparently inherited Oldowan technology and refined it into the Acheulean industry. Oldowan tools occur in Beds I–IV at Olduvai Gorge. Bed I, dated 1.85 to 1.7 mya, contains Oldowan tools and fossils of Paranthropus boisei and Homo habilis, as does Bed II, 1.7 to 1.2 mya. H. habilis gave way to Homo erectus at about 1.6 mya, but P. boisei persisted. Oldowan tools continue to Bed IV at 800,000 to 600,000 before present (BP). A significant change took place between Beds I and II at about 1.5 mya. Flake size increased, the length of bifacial edges (as opposed to single-face edges) occurred more frequently