TESTING NICHE STABILITY IN WESTERN INTERIOR SEAWAY CEPHALOPODS AND OTHER MOLLUSKS ACROSS THE ENVIRONMENTAL PERTURBATION OF OAE2

The Cenomanian-Turonian boundary (~ 94 Ma) has been widely studied in the paleobiological community as it is marked with a major environmental perturbation: Oceanic Anoxic Event 2 (OAE2). The magnitude of extinctions in response to this period of widespread marine anoxia is debated. However, another way that species and clades may respond to environmental change is through adaptation to new conditions. In this study we test this hypothesis by analyzing changes in the abiotic niche of surviving molluscan species and genera in the Western Interior Seaway of North America straddling OAE2. We focus on a set of 20 commonly occurring and abundant mollusks, including several cephalopods, that survive the Cenomanian-Turonian boundary and perform analyses at both the genus- and species-levels when possible. Niche characteristics were quantified using sedimentological proxies for abiotic conditions (e.g., proxies for water depth, substrate conditions, or oxygenation) following the guidelines for Paleoecological Niche Modeling (PaleoENM). The Ecospat package in the R programming language was used to compare independently-derived abiotic niche predictions in environmental space between the Cenomanian and Turonian to test for niche stability or change across the boundary. Although contrary to some recent findings of niche stability in Cenozoic and Ordovician taxa, only five out of 20 taxa studied here (two out of six cephalopods) demonstrate niche stability; the predominant style of niche change across the boundary was niche contraction. The presence or absence of niche stability is not consistent within higher taxonomic units (i.e., differences are observed among and between bivalves, gastropods, and cephalopods). Overall this study highlights the need for additional investigations into the ubiquity (or not) of niche stability in species and genera throughout the fossil record, and particularly in response to dramatic environmental perturbations.