A New Approach to Understanding the Early Miocene Paleoenvironment of Rusinga Island (Lake Victoria, Kenya): Using Leaf Margin Analysis, Leaf Area Analysis and Digital Leaf Physiognomy

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Larry Davis, Biology


Nearly one hundred years of field work has established Rusinga Island, Lake Victoria, Kenya as one of the most important Early Miocene (17-20 Ma) primate sites in Africa. In order to fully understand the patterns of Early Miocene primate evolution, it is critical to understand the paleoenvironments and paleoclimates in which these primates lived. In spite of the amount of paleontological work that has been conducted on Rusinga Island, results of paleoenvironmental and paleoclimatic studies have been contradictory. Furthermore, although there are abundant fossil plant remains on Rusinga, there have not been any studies that have attempted to reconstruct paleoclimate directly from fossil leaves. The correlation of the size and shape of woody dicot leaves with temperature and rainfall has been used to develop proxies for reconstructing mean annual temperature (MAT) and mean annual precipitation (MAP) from fossil leaves. Thus, the fossil leaves from Rusinga can be used to directly reconstruct the paleoclimate and paleoenvironment that existed during the evolution of Early Miocene primates, including the stem hominoid Proconsul.

A preliminary collection of 91 fossil leaves representing 28 distinct morphotypes (26 woody dicotyledonous (dicot) angiosperms and 2 monocotyledonous angiosperms) was made from a fossiliferous deposit near the top of the Grit Bed Member of the Hiwegi Formation near Kaswanga Point on Rusinga Island. I used the dicot morphotypes to estimate MAT and MAP using both univariate and multivariate methods. These analyses demonstrate that the Early Miocene MAT and MAP on Rusinga Island were ≥ 30°C and ~100-160cm, respectively. These estimates provide good preliminary evidence to suggest that the Early Miocene paleoenvioronment on Rusinga may have been a tropical-seasonal forest, and not a tropical woodland as reported by previous studies.

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