Paleobiogeography of the North American Late Cretaceous Western Interior Seaway: the impact of abiotic vs. biotic factors on macroevolutionary patterns of marine vertebrates and invertebrates

Abstract

My research investigates the relationship between ecology, evolution, and the environment in the fossil record. I hypothesize that abiotic environmental factors (e.g., climate, sea-level, ocean chemistry, and paleogeography) play a greater role in speciation, extinction, and distribution patterns than biotic factors (e.g., competition, mutualism). The effects of these factors can be observed in the fossil record as changes in species distributions, range sizes, and niche dimensions through time. Using GIS, paleoenvironmental reconstruction, and ecological niche modeling (ENM), I quantitatively investigated hypotheses of the relative influence of abiotic vs. biotic factors on macroevolution in three main studies of marine taxa from the Late Cretaceous Western Interior Seaway (WIS) of North America. The Late Cretaceous was a period of prolonged extreme and equable warmth; thus, this research has potential implications for species biology and biogeography in a projected future warmer world. The first study examined the influence of biotic interactions on patterns of extinction by competitive exclusion in marine vertebrates. Results indicated that competitive replacement was not a mechanism mediating extinctions. Instead other factors, such as environmental changes, likely controlled extinction patterns. The second study investigated the effect of large range size on survivorship and invasion potential in marine mollusks. No relationship between large range size and extinction resistance was recovered, however, endemic species with small range sizes were more likely to become invasive. These results suggest that some biogeographic "rules" (e.g., large range size confers extinction resistance and increased invasion potential) may not prevail under conditions of prolonged and equable global warmth. The last part of my research focused on improving methods for the application of ENM in the fossil record (paleo-ENM). In order to use ENM in the fossil record, detailed environmental layers must be reconstructed from sedimentological and geochemical proxies. Additionally, paleo-ENM requires high-resolution stratigraphic correlations of fossil-bearing formations and collection of large species' occurrence datasets that represent the full temporal and spatial extent of the species modeled. In order to produce high fidelity models, a standardized framework for paleoenvironmental reconstruction is required. Best practices are outlined for paleoenvironmental reconstruction, in addition to the contextual framework and important considerations necessary to appropriately apply paleo-ENM.