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Washington University in St. Louis (2011)

Taxonomic and Ecological Characterization of a Late Oligocene Mammalian Fauna from Kenya

Gutierrez Alvarez, Maria Mercedes

Titre : Taxonomic and Ecological Characterization of a Late Oligocene Mammalian Fauna from Kenya

Auteur : Gutierrez Alvarez, Maria Mercedes

Université de soutenance : Washington University in St. Louis

Grade : Doctor of Philosophy (PhD) 2011

Résumé
The Tertiary fossil record of Africa has offered several important primate species relevant to understanding crucial moments in primate evolution. Regrettably, the origin of apes has not been one of them. The reason for this was a large temporal gap of African fossil mammals that would theoretically provide information on the origin of apes and the faunal interchange between Africa and Eurasia that reshaped the continent’s species diversity. In this dissertation, I analyze a recently re-discovered fossil assemblage from the late Oligocene of Kenya (Nakwai/Losodok) that falls, according to current radiometric dating, within this temporal gap, and between the famous faunas from the Fayum (early Oligocene, Egypt) and Songhor (early Miocene, Kenya). The objectives of this dissertation are to : 1) describe the taxonomic and ecological structure of the late Oligocene fauna from Nakwai/Losodok, 2) to compare it taxonomically and ecologically to both early Oligocene and early Miocene faunal proxies, and 3) to use these comparisons to better understand the timing of the faunal interchange and the effects of environmental factors, if any, on the origin and evolution of typical Miocene apes. I accomplished these objectives by 1) comparing the taxonomic profile of all three faunas in terms of richness and diversity measures, 2) reconstructing body mass, dietary preference, and locomotion patterns for all mammals, and finally 3) characterizing all assemblages in terms of environmental attributes to better understand the evolutionary patterns in play. My results suggest that both Fayum and Nakwai/Losodok are similar faunas, dominated by archaic endemic mammals from Africa, implying that the faunal interchange between Africa and Eurasia did not occur until sometime between 24 – 20 Ma. I also found that Songhor stands out as a fauna that is environmentally different from the other two – a more forested environment with a higher proportion of arboreal and insectivorous mammals. No environmental correlation or evidence for niche competition was found that would explain the appearance of the first large body-sized catarrhine, Kamoyapithecus hamiltoni, in the late Oligocene of Kenya. However, a phyletic tendency of higher groups to evolve into larger body sizes was observed across the spectrum of Oligocene mammals.

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Page publiée le 15 mars 2019