Miocene Land Mammals from Panama: Refugium or Cradle of Biodiversity?

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Because of dense vegetation, access to fossil localities in the New World tropics (Neotropics) is very limited. As such, we have a poor knowledge of ancient Neotropical biodiversity. During the 20th century, Miocene sediments of the Cucaracha Formation exposed along the Panama Canal yielded a small, yet important collection of fossil land mammals, including rodents, bear-dogs, "true" canid dogs, horses, rhinos, oreodonts, and extinct deer-like animals. This ancient fauna provides an important glimpse of ancient Neotropical life during the Miocene.The paradox of this fossil mammal assemblage, however, is that it contains species that lived in North America during distinctively different times (i.e., combining different land-mammal ages). Thus, the oreodont that is unique to the early Miocene (~20 million years old) in North America co-existed in Panama with middle Miocene (15 million year old) rodents and deer-like species. Preliminary studies using rare earth element geochemistry, plus the known local biostratigraphy, indicate that this is not a taphonomically mixed (reworked) fauna, but represents sympatric species in this ancient Neotropical community. The fundamental question posed in this project, and the essence of its scientific merit, therefore, is to resolve whether this mammalian fauna from the Cucaracha Formation is:- 15 million years old, and therefore preserves early Miocene persistent "relicts," (refugium hypothesis), or;- 20 million years old, and has earlier occurrences of mammals than comparable faunas in North America (cradle of biodiversity hypothesis).This study will use 40Ar/39Ar geochronology and paleomagnetic stratigraphy to independently resolve the age of this mammalian assemblage and allow clarification of the "refugium" versus "cradle of biodiversity" hypotheses. Another goal of this project is to capitalize on recently authorized, new Panama Canal excavations over the next few years that will uncover a vast new sequence of Neogene rocks, including the mammal-bearing Cucaracha Formation. New fossils discovered during our field work will allow a better understanding of the ancient mammalian biodiversity of this region, as well as providing additional specimens to further test the hypotheses posed above.This project will involve field work along the Panama Canal to recover more fossils (e.g., by screen-washing) and associated geological samples for dating. In the US this project will involve museum comparisons of relevant Miocene mammals and laboratory analyses for 40Ar/39Ar and paleomagnetic determinations. In addition to PIs from the University of Florida, and collaborators from the New Mexico Museum of Natural History and Smithsonian Tropical Research Institute, this project will involve graduate students engaged in their own research. Broader impact/outreach activities will include public lectures and talks about this project as well as the potential of exhibits and citizen scientist activities that engage the public.