Simon A. F. Darroch, Michelle M. Casey, Gwen S. Antell, Amy Sweeney, and Erin E. Saupe (Oct 2020)
The paleogeographic ranges of fossil species may help us identify which species to protect in a future extinction event
“High preservation potential of paleogeographic range size distributions in deep time”
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Testing the preservation potential of geographic range size distributions from fossils
The geographic ranges of species are fundamental units of biogeography, combining to form present-day spatial patterns in diversity on a vast range of scales. Reconstructing the geographic ranges of species from fossils allows us to study how the ranges of species may have expanded, contracted, and shifted through time in response to a wide variety of global change events. Not only do these approaches (‘paleo-range reconstruction’) thus offer a way to examine the deep time processes that have sculpted present-day patterns in biogeography, but also – by examining to what extent past mass extinction events have preferentially selected against small- or large-ranged species – may offer us a way to predict which species may be most vulnerable in the ongoing biodiversity crisis (the ‘6th mass extinction’). Despite this, the distribution of fossils and fossil-bearing sediments changes significantly through time, and so the extent to which fossils can be used to re-create the geographic ranges of species is unknown. This study takes the present-day distributions of mammal species across the United States, and performs a suite of experiments that simulate both fossil records and the shifting distribution of fossiliferous sediments, to test whether the distribution of range sizes can be reliably preserved in fossils. The results show for the first time that the distributions of paleogeographic range sizes can be reconstructed with surprisingly high fidelity in fossils, even when the sediments that host these fossils are extremely scarce. This in turn suggests that the fossil record preserves an invaluable archive of species distributions in deep time, and that by identifying patterns of range-selectivity across past extinction events, paleontologists may be able to help predict which species are most at-risk as global ecosystems continue to deteriorate.
Abstract
Reconstructing geographic range sizes from fossil data is a crucial tool in paleoecology, shedding light on macroecological and macroevolutionary processes. Studies examining links between range size and extinction risk may also offer a predictive tool for identifying species most vulnerable in the ‘6th mass extinction’. However, the extent to which paleogeographic ranges can be recorded reliably in the fossil record is unknown. We perform simulation-based extinction experiments to examine: 1) the fidelity of paleogeographic range size preservation in deep time, 2) the relative performance of different methods for reconstructing range size, and 3) the reliability of detecting patterns of extinction ‘selectivity’ on range size. Our results suggest both that relative paleogeographic range size can be consistently reconstructed, and that selectivity patterns on range size can be preserved under many extinction intensities, even when sedimentary rocks are scarce. By identifying patterns of selectivity across Earth history, paleontologists can thus augment neontological work that aims to predict and prevent extinctions of living species. Lastly, we find that introducing ‘false extinctions’ in the fossil record can produce spurious range-selectivity signals; errors in the temporal ranges of species may pose a larger barrier to reconstructing range size-extinction risk signals than the spatial distribution of fossiliferous sediments.