IMPACT OF GEOGRAPHIC RANGE SIZE ON EXTINCTION SELECTIVITY IN LATE PALEOZOIC BRACHIOPODS OF THE NORTH AMERICAN MIDCONTINENT

Geographic range size has emerged as an important determinant of species’ extinction risk, however this pattern remains untested during times with extremely low rates of extinction. Here we test the impact of geographic range size on extinction and taxonomic duration using late Paleozoic brachiopods of the North American Mid-Continent. The late Paleozoic is a time of ‘sluggish’ evolution when global rates of origination and extinction are low resulting in very little turnover within brachiopods. Analyses were conducted using high-resolution spatiotemporal data for 175 brachiopod species, encompassing over 5000 spatially-unique occurrences. Data were obtained from the digitized collections of the University of Kansas, the Yale Peabody Museum, and the Paleobiology Database. Geographic ranges were reconstructed to the stage level using PaleoGIS v.4.2. Four different commonly-used metrics for geographic range size were employed: median area of a jackknifed convex hull; great circle distance; grid cell occupancy at 1° resolution; and latitudinal range of points. We evaluated the relationship between extinction patterns and geographic range size using binary logistic regressions for each stage with sufficient data, defined as greater than 5 extinctions. Geographic range size was correlated significantly with extinction in the Wolfcampian stage, but not consistently across all range size metrics. The median geographic range size of taxa that go extinct was smaller than the median range size of survivors in the Virgilian stage, but not consistently across all range size metrics. The small number of significant results may be due to low statistical power from the small number of extinctions that occurred at the boundary of each stage. This interpretation is supported by that fact that 1) the stages yielding significant results had the highest number of extinction events, and 2) there exists a significant positive correlation between median geographic range size and species duration. If correct, this pattern suggests that geographic range size still regulates extinction risk, even in scenarios where extinction rates dip so low we are unable to detect selectivity with confidence.