THE PALEOECOLOGY AND CHRONOLOGY OF THE MIDDLE MIOCENE HOMINOIDS FROM THE CHINJI FORMATION OF PAKISTAN.

摘要

The fluvial sediments of the Chinji Formation, Siwalik Group, northern Pakistan, preserve a Middle Miocene vertebrate fossil assemblage that includes hominoids of the genus Sivapithecus. This study provides a chronology for Sivapithecus using geomagnetic reversal stratigraphy and presents a reconstruction of its paleoenvironments based upon a study of the functional morphology of the bovid hind limb.; A series of laterally placed paleomagnetic columns that pass through the fossil localities are connected by reversal time lines and correlated with the Geomagnetic Reversal Time Scale. The oldest hominoids are found in the base of chron 11 at approximately 12 myr. Sivapithecus appears to be most closely related to the living orang-utan (Pongo), and this date of 12 myr may be close to the time of divergence between the Asian and African hominoid clades.; The reversal stratigraphy is used to investigate the sedimentation history of the basin, and sediment accumulation rates are shown to increase through time. Together these data suggest that the lower normal event of chron 10 at approximately 10.7 myr is of a longer duration than previously thought.; The morphology of the extant bovid hind limb is investigated to determine the functional linkage between morphology and habitat. Femoral head shape, shaft dimensions, and knee morphology are shown to be related to habitat, and the strength of these relationships are examined statistically with discriminant function analysis. Nine femoral characters support a significant separation among forest, woodland, and savanna habitat bovids. The morphological differences are related primarily to predator avoidance strategies, with more cursorial open habitat bovids displaying a limited degree of abduction and lateral rotation at the hip and more powerful extension across the knee.; This functional analysis is extended to the abundant fossil bovids from the Chinji Formation. These bovids are shown to have a unique morphology that most closely resembles bovids that today live in forested habitats. The habitat inference for the Chinji hominoids is then one of forested conditions. This habitat reconstruction suggests that Sivapithecus did not experience the adaptive shift to more open habitats that is believed to have played an important role in hominid origins.