Significant warming of Earth's climate in the near term seems increasingly likely. If significant enough, this climatic regime could, in the long term, come to resemble previous greenhouse intervals in earth history. Consequently, analysis of the fossil record during periods of extreme warmth may provide important lessons for species biology, including biogeography, in a much warmer world. To explore this issue, we analyzed the biogeographic response of 63 molluscan species to the long-term global warmth in the Late Cretaceous Western Interior Seaway (WIS) of North America, using Geographic Information Systems (GIS) to quantitatively measure changes in range size and distribution throughout this interval. We specifically considered the role that geographic range size played in mediating extinction resistance and invasion potential of these WIS species. We found no relationship between geographic range size and survivorship. However, endemic species with small range sizes were more likely to become invasive. Finally, mollusks did not experience a poleward shift in range out of the tropics during this warm regime. To the extent that these patterns are representative, and the WIS and taxa considered constitute a reasonable ancient analogue to a warmer future world, these results suggest that some biogeographic “rules” may not prevail under greenhouse conditions of long-term, equable warmth. They also suggest that other factors beyond geographic range size, including distinctive niche characteristics, may play quite important roles in species survival and invasion potential. This potentially complicates predictions regarding the future responses of extant species to long-term warming.

Myers_etal_SuppFig1Supplementary Figure 1. Histogram of log(geographic range) for all reconstructed ranges of molluskan taxa during the Late Cretaceous.Myers_etal_SuppTable1Supplementary Table 1. Species range size (reconstructed area and latitudinal extent) and outcrop area during each geologic stage. Coding for survivors and invaders: 1 = survived or invaded in the subsequent stage, 0 = did not survive or invade in the subsequent stage. Abbreviations of geologic stages: CEN = Cenomanian, TUR = Turonian, CON = Coniacian, SAN = Santonian, CAM = Campanian, MAA = Maastrichtian.Myers_etal_SuppTable2Supplementary Table 2. Contingency table analysis comparing biotic sub-provinces to survivorship and invasion potential. Endemic species are those that occur in only a single BSP. BSP = biotic sub-province and EC = endemic center of Kauffman 1984.Myers_etal_SuppTable3Supplementary Table 3. Contingency table analysis comparing survivorship and invasion potential to benthic vs. pelagic adult lifestyle and clade membership. Endemic species are those that occur in only a single BSP.