Paleobiogeographic and Paleoecologic Development of the Old World Savanna Paleobiome during the Neogene

Abstract

The study of paleobiogeographic development of Old World Neogene mammalian faunas has a long history. During the last decade further fossil data improvements and advancement in methods along with a focus on the context of paleoclimate change have offered new insights to reconstructing the paleobiogeographic development of the Negoene mammal communities. Recent studies produced with these new insights show that the development of mammal communities was influenced by changing climate and associated with the distribution of paleobiomes during the Neogene. The main objective of this study is build on these inspirational previous research by connecting local knowledge to broader scale perspectives for understanding the development and changes in the distribution of mammal communities between Eurasia and Africa during the Neogene. Large and small mammal fossil data were gathered during fieldwork campaigns in Anatolia and the most recent data from the New and Old Worlds database of fossil mammals were assembled. Genus-level faunal resembling index (GFRI), mean hypsodonty (mHYP), and genus-locality occupancy analyses were used to asses the paleobiogegraphic and paleoenvironmental development of the faunas and faunal provinciality, with a particular interest in understanding the biogeographic relationships between Eurasian and African late Miocene mammal communities. Fossil materials of two glirid species from the late Miocene of Anatolia are described, diet preferences are reconstructed with dental microwear analysis, and the species richness of the Gliridae family is evaluated. This study shows that the family Gliridae was influenced dramatically by changing climate dynamics during the middle and late Miocene of Eurasia. New magnetostratigraphic age correlation results and its faunal composition indicate that the Çorakyerler is a typical representative of the Pikermian chronofauna, demonstrating strong faunal affinity to the those of African early late Miocene sites. The faunal similarity results of the Çorakyerler locality triggered new questions about possible intercontinental biogeographic relationships between the open habitat adapted mammal communities between Eurasia and Africa. To address this question faunal similarity and mHYP anlayses were performed on a large dataset encompassing the entirety of the Neogene localities of the Old World. The Lower Nawata (Turkana Basin, Lothagam Fm, Kenya) fauna selected as a reference locality due to its closer geological age to the Pikermi and its unique faunal composition which represents an overlap of two groups; one consisting of late Miocene taxa, mostly dispersed from Eurasia, and the second consisting of the early appearance of East African Plio-Pleistocene faunal elements, most of which remained restricted to Africa. The combined results of this study illustrate that Neogene mammals were profoundly influenced by Neogene climate trends. Three significant paleobiogeographical stages in faunal developments of mammal communities in response to the changing environmental conditions are detected, supporting the conclusions of previous research. In the first stage, the pre-Neogene global tropical humid forest type ecosystem continued until the middle Miocene and patchy protosavanna-type habitats appeared towards end of the middle Miocene. By the second stage, increasing aridity heralded the appearance of savanna type environments and fauna by the end of the middle Miocene. This transition was characterized by the replacement of early and middle Miocene forest adapted large mammal communities by open habitat adapted species in vast regions of the Old World. As demonstrated in this study, by the beginning of the late Miocene Eurasian and African open habitat adapted faunas developed as one spatially and temporally connected entity, defined as the Old World savanna paleobiome (OWSP). Genus level faunal similarity analysis of the Lower Nawata in addition to Pikermi, Baode, and Çorakyerler localities suggests that the OWSP flourished under the influence of the middle and late Miocene global cooling and aridification that resulted in the spread of open habitats across vast continental areas. This extensive biome eventually fragmented into Eurasian and African branches most probably due to pressure from increased aridification in North Africa and Arabia during the latest Miocene. Its Eurasian branches had mostly disappeared by the end of the Miocene, but the African branch survived and contributed to the eventual development of the Plio-Pleistocene African savanna faunas. The third stage was characterized by increasing faunal provinciality and mHYP of Plio-Pleistocene mammal communities throughout the Old World.Neogene paleogeography of the Old World has been a significant parameter in explaining the dispersal of mammal faunas. However, reconstructing the development and biogeographic changes in faunal distributions of the mammal communities has been a complex matter mainly due to quality of the fossil record. Accumulations of chronologically and taxonomically revised and resolved data sets and advancements in methodologies during the last decade have provided better tools and broader perspectives to investigate paleobiogeographical development of the Neogene mammal chronofaunas.This study shows that high faunal and ecological similarity among the African and Eurasian chronofaunas indicate that these late Miocene mammal communities developed as a spatially and temporally interconnected entity within broadly similar climatic boundaries. Its Eurasian part disappeared at the Miocene-Pliocene boundary 5 million years ago, but the African branch survived and gave rise the modern African savanna fauna