Date of Graduation

5-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Environmental Dynamics (PhD)

Degree Level

Graduate

Department

Environmental Dynamics

Advisor/Mentor

Peter S. Ungar

Committee Member

Walter Manger

Second Committee Member

J. Michael Plavcan

Third Committee Member

Rene Bobe

Keywords

Social sciences, Biological sciences, Earth sciences, Australopithecus, Bovids, Dental texture, Hominin fossil, Microwear, Paleoenvironment

Abstract

Many researchers have suggested that Plio-Pleistocene climate change was a motive force for human evolution. The basic idea was that a shift toward drier, more open settings, led to adaptations for bipedality and the consumption of savanna resources, including large grazing mammals. However, more recent paleoenvironmental reconstructions suggest that Pliocene hominins occupied variable or mosaic habitats including both open and closed settings. Many techniques have been used to refine our understanding of the paleoenvironments of eastern Africa; however these have not led to consensus reconstructions. At Kanapoi, ecological diversity analysis indicates that at least part of the site was composed of closed woodland forest; however, taxonomic uniformitarianism of bovid taxa suggests a dry arid habitat. Similarly contradictory reconstructions exist for Allia Bay, with paleosol analysis and palynology suggesting a mosaic habitat dominated by savanna, and taxonomic uniformitarianism of faunal assemblages suggesting an environment composed of gallery forest, open woodland, floodplains and edaphic grasses. The Laetoli faunal assemblages have also led to varying reconstructions, with some suggesting habitats as disparate as open grassland and closed woodland. Hadar has been reconstructed as a shifting mosaic environment, with various proxies supporting different levels of habitat fluctuation. This dissertation aims to test these opposing hypotheses by bringing a new, independent dataset for the inference of diet by extension habitats of actual individuals in the days before death. I use dental microwear texture analysis to reconstruct ratios of graze to browse in the diet and therefore ecological contexts of fossil bovids from Kanapoi, Allia Bay, Laetoli and Hadar. This dissertation tests competing hypotheses concerning early hominin habitats at Kanapoi, Allia Bay, Laetoli and Hadar and how ecological settings may have changed over the temporal span of Australopithecus anamensis and A. afarensis. It also serves as an important test of the principle of taxonomic uniformitarianism, often applied to fossil fauna.

High resolution casts of 220 fossil bovids from the four sites and 575 extant African bovids were scanned for dental microwear textures using a white-light confocal profiler. Four adjacent scans of were collected from each specimen, resulting in a total work envelope of 204 x 276 µm. The scans were then analyzed using Toothfrax and Sfrax software packages and compared to a comparative database of extant bovids with known diets. The extant bovids collected for use in this study include 25 extant African taxa, representing the full obligate grazer-browser-frugivore continuum.

The extant bovids showed significant variation that separated the taxa predictably by known dietary category, with the exception of generalists and browser-grazer intermediates. Some variation was also noted within the dietary categories, suggesting seasonal and/or geographic variation. In general, browsing taxa had significantly higher values for complexity, heterogeneity and fill volume than grazing taxa, which evince higher values for anisotropy.

The microwear textures of the fossil taxa were compared to the extant comparative database and classified by diet. The Kanapoi and Allia Bay samples indicated that the bovids were primarily browsers or browser-grazers intermediates, suggesting the presence of more wooded habitats. The Laetoli sample is dominated by various levels of mixed feeding, although the presence of grazing taxa suggests a complex mosaic habitat at the site. Finally, the Hadar sample, divided into three hominin-bearing members, showed an increase in the number of grazing taxa over time. This suggests that there may have been gradual aridification at the site during the occupation of the australopiths.

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