...It's not the first time stone tools have been found with fossils of Paranthropus, a genus with several species that lived from about 2.8 million to 1.2 million years ago across Africa. In 1955, Louis and Mary Leakey discovered the Nutcracker Man, a skull with a robust jaw and teeth now classified as Paranthropus boisei, in the same 1.8-million-year-old layer of sediments as Oldowan tools. But Mary Leakey soon found a skull of Homo habilis (Latin for "handyman") in the same layer and thought that species, in our own genus, was a better fit as the principal toolmaker. Paranthropus, with...