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An extensive suite of isotopic data (δ 13 C, δ 15 N, and δ 18 O) from enamel apatite and bone collagen of adult male and female wild chimpanzees establishes baseline values for Pan troglodytes verus in a primary rainforest setting. The Ganta chimpanzee sample derives from a restricted region in northern Liberia. Diet is examined using stable light isotopes at three life stages—infant, young juvenile, and adult—and developmental differences are investigated within and between individual males and females. The isotopic data are very homogeneous with few exceptions. Juvenile females show consistent enrichment in 13 C relative to infants, while juvenile males do not. These data suggest that age at weaning may be more variable for male offspring who survive to adulthood than for female offspring. Alternatively, or additionally, the weaning diet of males and females may differ, with greater consumption of technologically extracted insects and/or nuts by young females. Metabolic differences, including growth and hormone-mediated responses, may also contribute to the observed variation. The Ganta chimpanzee data offer an independent and objective line of evidence to primatologists interested in the dietary strategies of the great apes and to paleoanthropologists seeking comparative models for reconstructing early hominin subsistence patterns. Despite the high diversity of dietary items consumed by chimpanzees, isotopic signatures of chimpanzees from a primary rainforest setting exhibit narrow ranges of variation similar to chimpanzees in more open habitats.

Several new postcranial elements of Sivapithecus from the Siwaliks of Pakistan are described. These include a distal femur from the U-level of the Dhok Pathan Formation, a navicular from the Chinji Formation, and seven manual and pedal phalanges from the Nagri Formation. The functional morphology of these elements adds new detail to the reconstruction ofSivapithecus positional behavior. Femoral cross-sectional geometry indicates that the shaft was adapted to support mediolaterally directed loading. Femoral condylar asymmetry and a broad but shallow trochlea are distinctly ape-like, revealing capabilities for both rotation and withstanding eccentric loading in the knee. The navicular is characterized by features relating to a broad mid-tarsus and broad distal articulations for the cuneiforms. It also lacks a navicular tubercle as in Pongo. These features suggest that the foot was capable of a powerful grip on large supports, with an inversion/supination capability that would permit foot placement in a variety of positions. The morphology of the new phalanges, including evidence for a relatively large pollex, similarly suggests powerful grasping, consistent with prior evidence from the hallux and tarsus. The functional features of the new specimens permit refinement of previous interpretations of Sivapithecus positional capabilities. They suggest a locomotor repertoire dominated by pronograde activities and also such antipronograde activities as vertical climbing and clambering, but not by antipronograde suspensory activities as practiced by extant apes.

The large-bodied hominoid from Moroto, Uganda has until recently been known only from proconsulid like craniodental remains and some vertebrae with modern ape like features. The discovery of two partial femora and the glenoid portion of a scapula demonstrates that the functional anatomy of Morotopithecus differed markedly from other early and middle Miocene hominoids. Previous studies have consistently associated the vertebral remains with a short, stiff back and with orthograde postures. Although the proximal femur more closely resembles the femora of monkeys than of apes and suggests a moderate degree of hip abduction, the distal femur resembles those of extant large bodied apes and suggests a varied loading regime and an arboreal repertoire that may have included substantial vertical climbing. The femoral shaft displays uniformly thick cortical bone, beyond the range of thickness seen in extant primates, and signifies higher axial loading than is typical of most extant primates. The glenoid fossa is broad and uniformly curved as in extant suspensory primates. Overall, Morotopithecus is reconstructed as an arboreal species that probably relied on forelimb-dominated, deliberate and vertical climbing, suspension and quadrupedalism. Morotopithecus thus marks the first appearance of certain aspects of the modern hominoid body plan by at least 20 Ma. If the suspensory and orthograde adaptations linking Morotopithecus to extant apes are synapomorphies, Morotopithecus may be the only well-documented African Miocene hominoid with a close relationship to living apes and humans.

Dividing the fossils usually assigned to the taxonHomo habilis sensu latointo two species (as most researchers now accept) necessitates a re-examination of their evolutionary relationships. A cladistic analysis of 48 of the most commonly-used cranial characters from recent studies of Pliocene hominid phylogeny and which distinguish two taxa withinH. habilis sensu latosuggests that these fossils have different evolutionary affinities. One taxon,H. habilis sensu stricto, is represented by KNM-ER 1813 and the fossils from Olduvai Gorge, and is most likely a sister group ofH. erectus. The other taxon,H. rudolfensis, is represented by KNM-ER 1470, and shares many derived characters with the australopithecines. A close analysis of the developmental basis of these characters suggests that many of the australopithecine similarities ofH. rudolfensisare likely to be homologies rather than homoplasies.

A distal tibia, YGSP 1656, from the early Late Miocene portion of the Chinji Formation in Pakistan is described. The fossil is 11.4 million years old and is one of only six postcranial elements now assigned to Sivapithecus indicus. Aspects of the articular surface are cercopithecoid-like, suggesting some pronograde locomotor activities. However, YGSP 1656 possesses an anteroposteriorly compressed metaphysis and a mediolaterally thick medial malleolus, ape-like features functionally related to orthograde body postures and vertical climbing. YGSP 1656 lacks specializations found in the ankle of terrestrial cercopithecoids and thus Sivapithecus may have been primarily arboreal. Nevertheless, the morphology of this tibia is unique, consistent with other interpretations of Sivapithecus postcranial functional morphology that suggest the locomotion of this ape lacks a modern analog. Based on the limited postcranial remains from S. indicus, we hypothesize that this taxon exhibited substantial body size dimorphism.

The magnetostratigraphy of the Chinji Formation (Siwalik Group, Pakistan) provides age estimates for the earliest occurrence of hominoids attributable toSivapithecus. This report documents a new earliest occurrence for the genus and provides age estimates for other Chinji Formation specimens described previously. These middle Miocene primates have figured prominently in discussions of the course and timing of hominoid evolution.Sivapithecus shares with the living orang-utan (Pongo) a number of derived craniofacial features indicating that they are sister taxa. The newly discovered specimens from the Chinji Formation therefore provide a minimum estimate for the time of the initial divergence between the Asian and African large hominoid clades. Large-bodied hominoids first appear in the Siwaliks at 12·5 m.y.a., with specimens preserving the derived craniofacial features dated at ∼ 12 m.y.a. This age estimate can be used to calibrate branching times of extant hominoids as determined from comparative molecular data.

The results of excavations in Miocene deposits at Maboko Island, Western Kenya, in 1973 are described. An account is given of the geology, and it is concluded that the deposits form part of a sequence of floodplain overbank deposits. These consist mainly of diagenetically altered sediments laid down in wet conditions and they differ from the more dry conditions indicated by the pedogenetically altered sediments, with the development of calcretes, to the north of Majiwa and Kaloma. The Maboko fauna contains abundant aquatic elements whereas the Majiwa and Kaloma faunas have greater terrestrial affinities, although the differences between the faunas is small. Faunal analysis and radiometric data reported here suggest that the age of the Maboko fauna is about 15 Ma.

The phylogenetic affinites of Ramapithecus have been debated since its initial description in the 1930s. The concensus view that Ramapithecus represents the earliest hominid has been challenged by new evidence from molecular studies and the discovery of fossils which include formerly unknown parts of the facial skeleton. These suggest that the “ramamorphs” may be more closely related to Pongo than to the African apes and hominids. The implications of this interpretation of the Miocene hominoids requires re-evaluation of certain previous assumptions about pongid and hominid evolution.

Craniofacial traits of two crania from Koobi Fora, Kenya, KNM-ER 1470 and KNM-ER 1813, are compared to determine the probability that they are from the same species, Homo habilis . It is argued that unless Homo habilis was significantly more sexually dimorphic than Gorilla gorilla , it is improbable that the two fossils can both be classified as Homo habilis . The creation of at least one new species is required to account for the morphological and metrical variation of Late Pliocene-Early Pleistocene Homo fossils in eastern Africa.

The magnitude of immunological differences between species has been used to estimate the time of divergence of lineages, especially among primates. Calibration of “clocks” based on immunological differences has relied heavily on data from Pakistan suggest that the lineages leading to Mus and Rattus diverged between 14 and 8 million years ago rather than 30 or more million years ago as suggested by techniques invoking constant rates of molecular evolution. Molecular analyses of pairs of mammal species which appear well documented paleontologically should be undertaken in order to expand our understanding of the tempo and mode of molecular evolution.

The period from 14 to four million years is poorly known in Africa, but during this time the Ethiopian fauna became established and hominids originated. The sedimentary sequence of the Tugen Hills in the Baringo area of Kenya provides important geological, environmental and plaeontological data concerning this interval. Concordant radiometric and palaeomagnetic determinations within the type section of the Ngorora Formation show that it spans more than 2 m.y., from 13 m.y.a. to less than 10 m.y.a., and from chrons 14 to 9. Other dates refine the calibration of the Younger Mpcsida, Lukeino and Chemeron units. Palaeontological results include the collection from the Ngorora Formation of one of the best Neogene macrofloras in Africa, and more fauna, including hominoids. No equids have been recorded older than 10 m.y.a. We also report new fauna from the more recent units.