Collaborative Research: Gateway to North America--the Great American Biotic Interchange (GABI) in Mexico and Origin of C4 Grassland

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Historical patterns of animal movements between the Americas are crucial to understanding current ecosystems and natural resources. The Great American Biotic Interchange (GABI) is a highly significant historical event of land animal movements between North and South America, triggered by the emergence of the continent-bridging Isthmus of Panama three million years ago. Isthmus formation substantially modified global ocean circulation, climate, and American ecosystems. Large animals such as giant ground sloths, armored glyptodonts, and terror birds moved northward and became an integral part of North American Ice Age ecosystems. North American elephant-like gomphotheres, horses, deer, camels, and carnivorans expanded into South America and triggered the most recent large mass extinction of native animals on that continent. A joint U.S.-Mexico team will investigate the timing and magnitude of these events in central Mexico, a critical gap in knowledge for GABI vertebrate and plant fossils. Integration of long-term fossil records with paleoenvironmental analysis will permit a more detailed reconstruction of the ecosystem reorganization events that led to today’s biodiversity patterns in the Americas. Broader impacts of the project include the development of Spanish and English museum exhibits and digital media, and research training opportunities for students from groups that are underrepresented in STEM fields.A team of vertebrate paleontologists, structural geologist, functional morphologist, phytolith botanist, and stable isotope geochemist will conduct field investigations in central Mexico to establish an integrated regional chronological framework using radiometric dates, fossil mammal biostratigraphy, and magnetostratigraphy to document succession of GABI immigrants. They will assess associated vegetation change using phytoliths and quantify relationships between herbivore diets and C4 vegetation origin, regional climate, and hydrological cycles in North America using isotope analysis of mammalian dental enamel and paleosol carbonates. Broad inter-continental mammal distributional patterns will be contextualized using network analysis to quantify deep-time biogeographic connectivity. Findings will be used to test hypotheses regarding phylogenetic relationships of key immigrant taxa, timing and delay in dispersal to high latitude regions, and climatic and environmental implications of regional C4 grassland expansion.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.