Most interpretations of early hominin phylogeny recognize a single early to middle Pliocene ancestral lineage, best represented by Australopithecus afarensis, which gave rise to a radiation of taxa in the late Pliocene. Here we report on new fossils discovered west of Lake Turkana, Kenya, which differ markedly from those of contemporary A. afarensis, indicating that hominin taxonomic diversity extended back, well into the middle Pliocene. A 3.5 Myr-old cranium, showing a unique combination of derived facial and primitive neurocranial features, is assigned to a new genus of hominin. These findings point to an early diet-driven adaptive radiation, provide new insight on the association of hominin craniodental features, and have implications for our understanding of Plio-Pleistocene hominin phylogeny.

Beta‐ray spectroscopy and radiotracer techniques have been used to study the transport of metal and oxygen during anodic oxidation. Both species are mobile during oxide film growth on Al, Nb, Ta, and W, but in Zr and Hf only oxygen transport is observed. Radiotracer measurements showed that the amount of metal dissolving in the electrolyte was usually less than 1% of the total oxidized, but that for Al it could be as high as 40%, depending on the current density and electrolyte used.

It is shown that from the energy spectra of He ions backscattered from aluminum, recorded before and after anodic oxidation, the thickness of the oxide films and the positions of ion‐implanted foreign atoms within the films can be determined. Information on the composition and uniformity of the films is also obtained. The scope, limitations, and precision of the method are predictable and are discussed. As model experiments the behavior of ion‐implanted noble gases was studied. The results agree with previous work and can be interpreted to show that, as expected, both aluminum and oxygen are mobile during the oxidation. The behavior of ion‐implanted alkali metals and halogens was also studied. These species were found to be mobile during oxidation and behaved in a manner consistent with their expected ionic charges.

The most complete early hominid skeleton ever found was discovered at Nariokotome III, west Lake Turkana, Kenya, and excavated in situ in sediments dated close to 1.6 Myr. The specimen, KNM-WT 15000, is a male Homo erectus that died at 12 +/- 1 years of age, as judged by human standards, but was already 1.68 m tall. Although human-like in many respects, this specimen documents important anatomical differences between H. erectus and modern humans for the first time.

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