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

由于茂密的植被，在新大陆热带（新热带）的化石地点是非常有限的。 因此，我们对古代新热带生物多样性的了解很少。 在世纪，沿着巴拿马运河露出的库卡拉卡组的中新世沉积物产生了一个小的，但重要的陆地哺乳动物化石的集合，包括啮齿动物，熊狗，“真正的”犬科动物，马，犀牛，oreodonts，和灭绝的鹿状动物。 这个古老的动物群提供了一个重要的一瞥古代新热带生活在中新世。然而，这个化石哺乳动物组合的矛盾之处在于，它包含了生活在北美的物种在明显不同的时间（即，结合不同的陆地哺乳动物年龄）。 因此，早中新世（约2000万年前）在北美所特有的奥形石在巴拿马与中中新世（1500万年前）的啮齿动物和鹿类物种共存。 利用稀土元素地球化学的初步研究，加上当地已知的生物地层学，表明这不是一个埋藏混合（改造）动物群，但代表同域物种在这个古老的新热带社区。 因此，该项目提出的基本问题及其科学价值的本质是解决来自Cucaracha组的哺乳动物群是否：-1500万年，因此保留了中新世早期的持久性“遗迹”，（避难所假说），或;- 两千万年前哺乳动物的出现比北美洲的同类动物群要早这项研究将使用40 Ar/39 Ar地质年代学和古地磁地层学来独立地解决这个哺乳动物组合的年龄，并允许澄清“避难所”与“生物多样性摇篮”的假设。 该项目的另一个目标是在未来几年内利用最近授权的新的巴拿马运河挖掘，这将揭示一个巨大的新的新近纪岩石序列，包括哺乳动物的Cucaracha地层。 我们在野外工作中发现的新化石将使我们能够更好地了解该地区古代哺乳动物的生物多样性，并提供额外的标本来进一步验证上述假设。该项目将涉及沿着巴拿马运河进行野外工作，以恢复更多化石（例如，通过筛洗）和相关的地质样品用于测年。 在美国，该项目将涉及博物馆对相关中新世哺乳动物的比较，以及对40 Ar/39 Ar和古地磁测定的实验室分析。 除了来自佛罗里达大学的PI，以及来自新墨西哥州自然历史博物馆和史密森热带研究所的合作者外，该项目还将涉及从事自己研究的研究生。 更广泛的影响/外联活动将包括关于该项目的公开讲座和讲座，以及吸引公众参与的展览和公民科学家活动的潜力。

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.