Niki Garrett is a PhD candidate from the University of Minnesota. She was awarded a Leakey Foundation research grant in the fall of 2013 for her project entitled “Compound specific paleoecology of Early Miocene hominoids from East Africa.” Here is a brief description of her research followed by a report from the field.
I am interested in the relationship between ecological/climate change and primate evolution. The aim of this study is to obtain detailed paleoenvironmental reconstructions of the Early Miocene (~15-20 Ma) fossiliferous sediments on Rusinga Island, Kenya, in order to clarify our knowledge of the habitats that supported some of the earliest fossil apes. The fossil deposits on Rusinga Island contain some of the richest samples of Early Miocene floral and faunal communities, including many partial skeletons of the putative hominoid Ekembo (Proconsul), fossils from the less well-known catarrhines Limnopithecus and Nyanzapithecus, and three strepsirhine genera Komba, Progalago, and Mioeuoticus. These sites provide an excellent setting to examine the adaptation and diversification of catarrhines and early hominoids, which is a necessary foundation for our understanding of the evolutionary history of all apes including humans.
Relatively new molecular proxies will be utilized in this study to augment previous paleoenvironmental reconstructions. Specifically, compound specific hydrogen and carbon isotope analysis of plant leaf waxes (n-alkanes and n-alkanoic acids) preserved in the paleosol and lacustrine sediments. In a C3-only ecosystem, such as those found in the Early Miocene, carbon and hydrogen isotope analyses have the ability to inform our understanding of the density or open/closed nature of the local habitats. This research will provide a paleoenvironmental context for not only this important primate community, but also the extensive mammalian faunal community, as well as to provide documentation of any temporal or spatial changes in habitat during the Early Miocene.
The Leakey Foundation research grant afforded me the opportunity to travel to Rusinga Island, Kenya for a third research trip this past August. First explored in the 1930s by members of the third East African Archaeological Expedition led by L.S.B. Leakey and D.G. MacInnes, fossil deposits on Rusinga Island contain some of the richest samples of Early Miocene floral and faunal communities, including the largest known collection of the primitive hominoid Ekembo (Proconsul). Vertebrate fossils from more than 90 species of mammals are known from the Early Miocene Rusinga Group, which comprises in stratigraphic order, the Wayando Formation, Kiahera Formation, Rusinga Agglomerate, Hiwegi Formation, and Kulu Formation. Renewed research has provided important new insights into the geological and paleoenvironmental context for these deposits including new age constraints for the Kulu Formation (~15-17 Ma) and for older formations (~18-20 Ma). Although decades of research at these sites have produced multiple paleoenvironmental studies, a clear consensus has yet to be reached regarding the ecological context for Rusinga’s early apes and other catarrhine primates. Most previous paleoenvironmental research has focused on the highly fossiliferous Hiwegi Formation. The aim of my research is to obtain detailed paleoenvironmental reconstructions for the entire sequence of Early Miocene fossiliferous sediments allowing for documentation of any temporal changes and providing a detailed picture of the habitats utilized by these primates at a critical period in the evolutionary history of hominoids.
The primary goal of this trip was to collect lacustrine and paleosol samples from the Kulu and Kiahera Formations for compound (n‑alkane and n-alkanoic acid) specific carbon and hydrogen isotope analyses (CSIA). Compared to previous field seasons, this trip was very quick and involved a relatively small field team. In addition to three Kenyans (Francis Sina Muteti from the National Museums of Kenya, and Joshua Siembo and Collins Ouma Ogongo from Rusinga Island), I traveled with Dr. Lauren Michel (geologist, current postdoctoral researcher at Southern Methodist University, Dallas, Texas) and Joel Torgeson (field assistant, undergraduate at the University of Minnesota). The six of us spent a total of nine days at various sites around the island assessing the suitability of the formations and deposits for this, and future, research. One of the main factors to be considered when identifying and collecting sediment samples for CSIA are modern contaminants. Sediment samples need to be completely free of modern roots and other plant materials. At some of the Rusinga Island sites, we found this to be nearly impossible making those sites/sediments unsuitable for this specific type of research. On one day in particular, this was a pervasive problem. We spent one Sunday at multiple sites within two localities, and I was unable to collect a single suitable sample for CSIA. It was noted that the roots appeared to be following the specific layers I was targeting, and no amount of trenching into the hills appeared to uncover sediments without visible modern plant roots – the paleosol sediments were as appealing to the plants as they were to me (although for very different reasons), however the plants got there first!
In the end, I was able to find multiple suitable sampling sites free of modern plants. I collected samples of the lacustrine deposits in the Kulu and Kiahera Formations. We were also able to identify and describe ~2.3 meters of exposed paleosol in the Kiahera Formation where I also collected CSIA samples. I collected these samples using a protocol that ensures they are not contaminated by other sources of organic matter, such as oils from my hands, sunscreen, or plastic bags.
The next step in this research is to travel to the Lamont-Doherty Earth Observatory (Columbia University, NY) where I will extract and isolate the n-alkanes and n-alkanoic acids from the sediments. Long, straight‑chain (i.e., normal, n‑) alkanes and alkanoic acids are the primary components of the protective waxes that coat the leaf surface of almost all land plants. Because these compounds are extremely environmentally persistent in sediments over geologic time and are resistant to biodegradation, they serve as an exceptional proxy for ancient vegetation in terrestrial or terrigenous sediments. Once these compounds are extracted and purified, I will analyze the abundance and distribution of the alkanes and alkanoic acids, as well as the carbon and hydrogen isotopic compositions of the target compounds. These steps will provide me with information on how “open” or “closed” the local habitats were on Rusinga Island during this period, allowing for a robust evaluation of the variability in the C3 ecosystems inhabited by the Early Miocene catarrhines including the earliest hominoids.