Collaborative Research: Elements of an extinction: Exploring the delayed Caribbean extinction with stable isotopes and trace elements

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Biologists warn that the current degradation and fragmentation of ecosystems will lead to extinctions long into the future -- a process dubbed 'Extinction debt' --but making accurate predictions requires a much better understanding of how extinctions occur over long-term time scales. This project will dissect the Plio-Pleistocene extinction event (1-2 Myr) in the southwestern Caribbean (SWC) to examine the relationship between environmental perturbation and extinction rate. During the Plio-Pleistocene event, extinction rates peaked between 35 and 100% in a variety of marine taxa across the Caribbean. Taxa better adapted to nutrient-rich conditions were impacted most. Thus, the extinction is often attributed to declining planktic nutrients in Caribbean water due to isolation from the Pacific after the closure of the Central American Isthmus. The extinctions lagged closure by 1-2 Myr, however, leading some researchers to attribute increased extinction rates to climate change associated with the onset of northern hemisphere glaciation. This study will integrate biotic and geochemical data to reveal the direct causes of the Caribbean extinction event and evaluate the evidence for the perceived delay using established and new paleoenvironmental proxies and the unprecedented breadth of sampling and depth of taxonomic analyses provided by the Panama Paleontology Project (PPP). Three hypotheses will be tested: (1) Doomed taxa survived in nutrient-rich refugia that persisted after Isthmus closure; extinction occurred when refugia diminished sufficiently. (2) Extinction was driven by cooling related to northern hemisphere glaciation. (3) Temporary survival of doomed taxa was unrelated to changes in nutrients or temperature, suggesting stochastic processes were responsible. To accomplish this, we will generate high-resolution stable isotopic (18O/16O, 13C/12C) profiles of ~90 gastropod shells from 26 fossil localities in the SWC dating between 5 and 1.4 Ma, supplemented by clumped isotope (13C18O/12C16O) and trace element (P/Ca, Sr/Ca, Ba/Ca) analyses, to determine past local temperature and nutrient availability. This project will be the first to establish a well-constrained environmental system using the Tropical American fossil record and multiple high-resolution geochemical proxies to test a range of evolutionary hypotheses. These include the processes responsible for speciation, extinction, niche expansion, and evolutionary maintenance of sexual reproduction. Uniting biotic data with detailed paleoenvironmental data will reveal the root cause of the most geologically recent marine extinction and provide a real-world example with which to test models of the process of large-scale biodiversity loss. The modern anthropogenic fragmentation of natural habitats and populations mirrors the refugia that are purported to have delayed the extinction of SWC taxa in the Pliocene. Our data will evaluate this hypothesis and demonstrate whether this loss in biodiversity was directly related to environmental changes.The project will integrate a Panama-based field experience into the undergraduate capstone course of the Environmental Programs in Geoscience at Texas A&M University (TAMU). Students will work in groups and conduct paleobiology and stable isotope research on samples they collect in Panama, and sample and analyze at TAMU. In addition to presenting results, students will write, peer-review, and revise research papers. The project will train a post-doctoral fellow and graduate student in interdisciplinary science and research mentoring. Finally, research findings will be presented at major national and international meetings and published in premier journals.