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Stable isotope and molecular data suggest that C4 grasses first appeared globally in the Oligocene. In East Africa. stable isotope data from pedogenic carbonate and fossil tooth enamel suggest a first appearance between 15-10 Ma and subsequent expansion during the Plio-Pleistocene. The fossil enamel record has the potential to provide detailed information about the rates of dietary adaptation to this new resource among different herbivore lineages. We present carbon isotope data from 452 fossil teeth that record differential rates of diet change from C3 to mixed C3/C4 or C4 diets among East African herbivore families at seven different time periods during the Late Miocene to the Pliocene (9.9-3.2 Ma). Significant amounts of C4 grasses were present in equid diets beginning at 9.9 Ma and in rhinocerotid diets by 9.6 Ma, although there is no isotopic evidence for expansive C4 grasslands in this part of the Late Miocene. Bovids and hippopotamids followed suit with individuals that had C4-dominated (>65%) diets by 7.4 Ma. Suids adopted C4-dominated diets between 6.5 and 4.2 Ma. Gomphotheriids and elephantids had mostly C3-dominated diets through 9.3 Ma. but became dedicated C4 grazers by 6.5 Ma. Dein otheriids and giraffids maintained a predominantly C3 diet throughout the record. The sequence of differential diet change among herbivore lineages provides ecological insight into a key period of hominid evolution and valuable information for future studies that focus on morphological changes associated with diet change. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the morphology of the vertebral remains of the KNM-BG 35250 Nacholapithecus kerioi individual from the Middle Miocene of Kenya. Cervical vertebrae are generally large relative to presumed body mass, suggesting a heavy head with large jaws and well-developed neck muscles. The atlas retains the lateral and posterior bridges over the vertebral artery. The axis has a robust dens and a large angle formed by superior articular surfaces. The thoracic vertebral specimens include the diaphragmatic vertebra and one post-diaphragmatic vertebra. The thoracic vertebral bodies are much smaller that those of male Papio cynocephalus, whereas many of the dorsal elements are large and robust, exceeding those of male P. cynocephalus. Lumbar vertebral bodies are small relative to body mass, craniocaudally moderately long, and have a median ventral keel. The transverse process is craniocaudally long and arises from the widest part of the body cranially and the pedicle above the inferior vertebral notch caudally. Anapophyses are present in one of the preserved lumbar vertebrae. The postzygapophyses are thick dorsoventrally. These lumbar features are broadly shared with Proconsul. However, the base of the spinous process is longer and more caudally positioned in N. kerioi compared to Proconsul, and is more similar to the condition in Pongo. They are not dorsally (or moderately caudally) directed as is seen in P. nyanzae, Pan, and most other extant primates. A caudally directed spinous process does not permit a broad range of spinal dorsiflexion. The presumed stiff back in N. kerioi suggests a different locomotor repertoire than in Proconsul. Morotopithecus bishopi, although not possessing the same features, exhibits another morphological suite of characters for lumbar stiffness. Diverse functional adaptations of the lumbar spine were present in African hominoids during the Early to Middle Miocene. [Copyright &y& Elsevier]