Early Hominin Paleoecology

10. Plants and Protopeople

355 10 Plants and Protopeople: Paleobotanical Reconstruction and Early Hominin Ecology Jeanne Sept Vegetation was a core component of the early hominin landscape, whether providing hominins with staple plant foods, shade, and arboreal refuge, or creating habitats and hiding places for their predators. Trying to reconstruct and understand the paleoecological relationships between hominin species and the plant communities in which they lived is a fascinating scientific challenge because it is dependent on the integration of so many types of modern and ancient data. It is also challenging because direct fossil evidence of ancient plants and vegetation patterns is relatively rare, compared to the vertebrate or invertebrate fossil records; thus many of our reconstructions of ancient vegetation patterns are based on indirect analogies with modern contexts. While the fossil record suggests that plant taxa have evolved significantly through the Cenozoic, relatively few morphological changes are apparent in individual plant taxa during the last 7 myr (million years) of hominin evolution in Africa. This allows paleobotanists to use morphological comparisons to identify ancient macro- and microbotanical remains with relative precision. It also allows paleobotanists to make uniformitarian assumptions that the basic physiological processes and ecological principles fundamental to plants today can be applied to interpret the paleobotanical record. It thus forms the basis for our ability to understand plant variety, abundance, and distribution in the past. DOI: 10.5876/9781607322252:c10 jeanne sept 356 For example, when considering evidence for the plant-food diet of early hominins, we can reasonably assume that the fruit of an ancient fig would have had similar nutritional properties to the fruit of closely related modern figs,and would have been eaten when available by hominins, just as living primates and people commonly feed on raw figs today (Peters and O’Brien 1981). We can make comparable inferences about other nutritional attributes of plant taxa that hominins would have encountered.Considering questions of habitat on a larger scale, while it is clear that modern vegetation patterns cannot be used as direct analogs for ancient environments, an understanding of the ecological structure and diversity of modern vegetation types in relation to local climate and soils allows us to develop hypotheses about the attributes of vegetation that would have grown under comparable conditions in the past. Such models of vegetation composition and physiognomy then can be tested against different types of direct and indirect paleobotanical evidence. BACKGROUND TO PLANT STUDIES IN AFRICA Vegetation Patterns Before considering the different methods available for reconstructing ancient plant communities and paleoecological relationships, it is useful to quickly review the current vegetation patterns in Africa. Africa is such a large continent , straddling the equator and stretching to temperate regions in both the northern and southern hemispheres, that its vegetation includes a number of distinct vegetation types and floral zones (White 1983). Vegetation is shaped by the intersection of climatic conditions with the regional and local landforms, particularly the topography and soil chemistry and structure. The bulk of the African continent is characterized by low-altitude, gentle topography. The only significant highlands occur as ancient, metamorphic folded mountain belts on the northern and southern tips of the continent, and the eastern volcanic highlands that flank the Rift Valley. Significant altitude creates temperature gradients in the highlands, resulting in strong vertical zonation in montane vegetation types, especially in East Africa. These altitudinal vegetation zones range from moist evergreen and deciduous forests on the flanks of the mountains, through floristically distinctive belts of montane forest, including bamboo, to zones of ericaceous (plants requiring acidic soil) heath and moorland on the highest peaks above the treeline, such as the Ruwenzoris, Mount Kenya, and Mount Kilimanjaro. Climate patterns produce dramatic differences in rainfall across Africa. The tropical air masses track from west to east, bringing moist equatorial air from plants and protopeople 357 the Atlantic and producing considerable rainfall across the center of the continent , up to the margins of the eastern highlands. As the westerlies rise over the highlands, they release most of their remaining moisture on the western flanks of the mountains, creating a rain shadow in the Rift Valley to the east. Shifting in latitude either north or south from the equator, the climate is drier. In the mid-latitudes the equatorial air converges with easterly prevailing winds, creating an Intertropical Convergence Zone (ITCZ). Storms are generated along the ITCZ in both hemispheres, and the path of the ITCZ shifts north and south annually...