Collaborative Research: 100 million Years of Biotic and Tectonic Evolution in the Western Branch of the East African Rift System

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The fossil record of sub-Saharan Africa holds keys for testing a range of paleobiogeographic hypotheses that assess how large-scale landform dynamics have influenced biotic evolution over the past 100 million years. Annual expeditions since 2002 to the Rukwa Rift Basin in southwestern Tanzania have revealed a remarkable diversity of new Cretaceous and Cenozoic terrestrial and freshwater vertebrates. Moreover, the discovery and characterization of novel tectono-sedimentary relationships within the Western Branch of the East African Rift System (EARS) have firmly established the importance of this region for examining the interplay between tectonic events and macroevolutionary patterns, encompassing the origin, diversification, paleobiogeography, and extinction of major terrestrial vertebrate clades on continental Africa from the Mesozoic well into the Cenozoic Era. This research group aims to explore the relationship between landform evolution and biotic response in deep time at both local and regional levels, sampling time-distinct geological units to document faunal and floral dynamics at key points in eastern Africa.New Cretaceous discoveries from this project represent all major vertebrate groups, including novel mammals, dinosaurs, and crocodyliforms. The team has concurrently identified the only late Oligocene terrestrial and freshwater assemblage south of the equator, preserving a novel and diverse fauna characterized by spectacularly preserved examples of fishes, snakes, turtles, crocodylians, birds, and a diversity of mammals. Their field area is unique in encompassing both sides of the K/Pg boundary within a restricted geographic area. Multi-modal geochronologic approaches have been applied to reveal that Cenozoic activation of the Western Branch of the EARS initiated at least 14 million years earlier than previously estimated, penecontemporaneously with the better characterized Eastern Branch. Taken together, these results underscore the significance of this region for testing paleobiogeographic hypotheses regarding the origin and distribution of Gondwanan vertebrates during the geologically and biologically dynamic period from the Cretaceous into the Cenozoic. To date the team has explored only a fraction of the deposits within the RRB, and has recently initiated exploratory surveys into adjacent basins (e.g., the Malawi Rift Basin). The goals of this proposal are: 1) to provide explicit stratigraphic, sedimentologic, and depositional context for strata in the RRB and hitherto unexplored adjacent sub-basins, together with precise age constraint for fossil-bearing intervals; 2) to further characterize the interplay between tectonic activity and sub-basin development/drainage patterns that resulted in these rare terrestrial/freshwater assemblages from sub-equatorial Africa; and 3) to conduct detailed anatomical and phylogenetic studies on fossils recovered from the field, using these data to assess competing macroevolutionary hypotheses related to the origin, diversification, paleobiogeographic distribution, and extinction patterns of late Mesozoic and Cenozoic vertebrate groups. Understanding how organisms respond to environmental change is of critical importance, particularly considering that today?s ecosystems are undergoing an unprecedented rate of change. Information from the fossil record plays an essential role for providing a deeper perspective on how environmental changes influence animal and plant species over time. This project provides important new data from an interval spanning 100 million years of Earth's history, through geological and paleontological exploration of a critically undersampled region on the African continent. Large portions of the large East African Rift System, particularly in southwestern Tanzania, have received relatively little scientific attention, yet they record dramatic changes in landform (e.g., rifting, uplift topography, surface water flow), climate change, and the impact of these events through time for the region?s resident animals and plants. This project examines three distinct time intervals within the rift system, integrating geological data with paleontological data to assemble a precisely dated picture of fossil organisms within the environmental settings that entombed them. Field teams consisting of students and faculty from several US institutions will conduct expeditions in the study area to collect paleontological data (fossils) and geological samples (for age-dating of rock units and sedimentary rock analyses that document environmental setting). These data will provide important new information on environmental change and the evolution of past life on the planet. This research will (1) provide new paleobiological data from eastern Africa at three key points in geologic time; (2) utilize new and more precise laboratory approaches to constrain the age and environmental conditions of the geological settings; (3) offer numerous opportunities for US researchers (students and faculty) to participate as part of an international, interdisciplinary research group focused on integrating field and laboratory approaches for characterizing biodiversity and environmental conditions in deep time, and (5) disseminate results to scientific and public audiences via conference presentations, websites, and museum venues in the US and internationally. This research will impact our understanding of animal and plant distributions (biogeography), ecological conditions of past environments (paleoecology), and provide fundamental insights into key topics in evolutionary biology (e.g., adaptation, extinction). It will also contribute baseline data for use by other disciplines, including geophysics/tectonics, climate studies, computer modeling, conservation, and STEM education in biological and Earth sciences.This program of work is jointly funded by the Sedimentary Geology & Paleobiology Program of the Geosciences Directorate, and by the International Science & Engineering Program of the Office of International & Integrative Activities.