With National Science Foundation support, Drs. Sponheimer, Ungar, and Passey and an international team of colleagues will investigate the environmental context of human evolution. The team includes researchers from the U.S., Canada, Israel,and South Africa who will use their expertise in vertebrate paleontology, isotopic geochemistry, wildlife ecology, and human paleobiology to study human paleoecology through the lens of rodent dietary ecology. It has long been recognized that the ecological diversity and small home ranges of rodents make them particularly useful tools for reconstructing past environments. However, studies of rodent faunas have traditionally made assumptions about the ecology of fossil specimens rather than measuring dietary attributes directly. In contrast, this project will directly determine rodent diets to investigate the relationship between modern rodent dietary ecology and habitats, and then apply this knowledge to the South African human fossil record.
Diet will be studied using dental microwear texture analysis, stable carbon isotope analysis, and strontium isotope analysis. The first two provide direct measures of dietary attributes (e.g., mechanical properties of foodstuffs, tree fruits/leaves versus grasses), while the last allows determination of where animals lived on the landscape, potentially resulting in more spatially-refined environmental reconstructions. The project will have three phases. In the first phase, the research team will conduct an extensive study of the relationship between modern rodent diets and habitat features. In the second phase, the team will determine the degree to which the diets of modern rodents from owl roosts reflect local habitats, essentially investigating the degree to which owl predation biases the environmental signal. The last phase will entail application of this knowledge to fossil sites in and around the Sterkfontein Valley, South Africa that are from ~2.5 million to ~700 thousand years old.
The intellectual merit of this project is that it will provide new evidence of early hominin ecology and environments, and in so doing, will help address questions about hominin adaptations and evolution. For instance, did humans putative ancestors, big-brained early Homo, emerge in Africa only after significant deterioration of preferred enviroments, and did such environmental change contribute to the extinction of our smaller-brained, and presumably less adaptable, evolutionary "cousin" Paranthropus? It will also establish a firmer basis for using rodent dietary ecology to reconstruct paleoenvironments, which will be of broad utility at other archaeological and paleontological sites. In addition, it will mark the first time that multiple techniques have been used to investigate the intersection of animal diets, abundances, and environmental/climatic parameters over long (2 million year) timescales. Furthermore, the analytical developments to be made as part of this project will be of use for fields beyond archaeology including biological anthropology, geology, geochemistry, conservation ecology and paleontology.
The broader impacts of this study are that it will foster international collaboration, provide training for students from underrepresented groups, enrich undergraduate teaching and graduate mentoring, and be used as a platform for bettering public understanding of science and technology. This is especially relevant for the University of Arkansas, a public university in an underfunded EPSCoR State.
Reconstructions of environments in the past, and how those changed over time, are important keys to understanding how and why our ancestors evolved as they did. When the environment changes, species must adapt to new conditions or they may face extinction. And there are a great many research studies directed at trying to infer past habitats, especially those of Africa, over the past six million years or so, to help us better understand the circumstances of human evolution. The study reported on here has focused on developing a new proxy for reconstructing habitats of our ancestors based on dental microwear of rodents and shews. Dental microwear is the study of microscopic use-wear on teeth. And previous studies of microwear of a variety of mammals shows that the patterns vary in a predictable way with diet. This study considered rodents and shews because they are ubiquitous at many fossil human ancestor sites, and they tend to eat foods closely associated with the microhabitats they live in. The basic idea is that if we can associate a pattern in living rodents and shrews with specific habitats, we look to microwear of fossil ones to infer past environmental conditions at sites where human ancestors lived (alongside the micromammals). There were two main elements to this study: 1) Smithsonian Institution Rodents and Shrews), and 2) Free State and Lesotho Rodents. Several hundred specimens were examined at the Smithsonian in Washington DC. These skeletal collections come from many different highly-distinct habitats (desert to rainforest, equator to arctic), and we have used them to look for differences within and between species related to environment. Results to date indicate that individual species show specific patterns, and that those patterns depend in part on the vagaries of diet differences and habitat differences. Work on the incisors is completed, and work on the molars is ongoing. Several hundred specimens were also examined at the National Museum in Bloemfontein, South Africa. This collection includes five rodent species from very subtly varying environments, with finer-scale differences grading over space in vegetation, rainfall, altitude, soil type, etc. Work on these specimens is progressing – microwear data have been collected for three of the five species so far, and preliminary results suggest that differences between species are greater than those within species between environments. The funds for this project were used largely for collecting tooth impressions of specimens at the museums, and for generating data on their microscopic wear to relate pattern to environment. To date six students have/are using these data as integral parts of their theses (undergraduate and graduate), and they have served in training them in analytical techniques and interpretation. Two honors theses have been completed and successfully defended, a master’s thesis is in progress and nearly done, and two additional projects by PhD-level students are pending completion now. We have presented results at the American Association of Physical Anthropologists annual meetings, and the first of several anticiapted peer-reviewed journal papers is already published on the results.
