Potential Impacts of Transitional Wetland Habitats on Megafaunal Distributions in North America during the Last Deglaciation

Late Quaternary megafaunal extinctions in North America represent a major loss of large-bodied mammals, yet the ecological processes underlying species-specific decline remain unclear. In particular, the role of short-term habitat changes during the last deglaciation has received less attention than climatic or anthropogenic explanations. Palaeoecological studies indicate that mid-latitude North America experienced extensive but short-lived wetland expansion during the Bølling–Allerød interstadial (~14.6–12.8 ka), driven by meltwater discharge from the retreating Laurentide Ice Sheet, followed by rapid wetland contraction around the onset of the Younger Dryas. In this study, we examine how these wetland changes as major habitats are reflected in megafaunal distribution patterns across the Bølling–Allerød to Younger Dryas transition. We compile genus-level fossil occurrence data from publicly available databases and integrate them with spatial reconstructions of deglacial wetland extent. Using time-sliced analyses between approximately 15 and 11 ka, we explore changes in geographic range, spatial clustering, and distributional fragmentation of megafaunal taxa. Our analyses focus on wetland-associated taxa such as Mammut (mastodon), Castoroides (giant beaver), and Cervalces (stag-moose), and compare their spatiotemporal distribution patterns with those of non-wetland-associated megafauna. Preliminary results show that wetland-associated taxa tend to display more spatially clustered and persistent distributions during the Bølling–Allerød, when wetland extent was greatest. Following the onset of the Younger Dryas, these taxa exhibit increased fragmentation and range contraction. In contrast, non-wetland-associated taxa show weaker and less consistent changes through time. These results suggest that transient wetland landscapes were closely linked to short-term distributional stability in certain megafauna prior to rapid decline, and motivate further analyses to better evaluate habitat-related mechanisms during the last deglaciation.