The causes and consequences of the Pliocene marine megafaunal extinction event

The late Pliocene marine megafaunal extinction event was a major episode of biodiversity loss for large-bodied marine vertebrates. The selective extinction of marine megafauna during this event is particularly relevant to modern ecosystems, as extant marine megafauna face increased extinction risk. However, the ecological consequences of the Pliocene marine megafaunal losses on ecosystem structure and function, and the primary extinction drivers behind them, remain unresolved. This thesis addresses these important knowledge gaps. Trait-based reconstructions of North Atlantic pelagic food webs were generated for pre- and post-extinction intervals. Despite substantial taxonomic losses, including the extinction of a giant apex predator, ecosystem structure, function and trophic organisation remained broadly stable across this event. Although minor structural shifts occurred, overall, food webs appeared to have been resilient to megafaunal losses, potentially due to trophic redundancy. Extinction rate analyses across the Neogene and Pleistocene were then used to examine regional variation in extinction rates across ocean basins. Significant spatial variation emerged, with the North Atlantic exhibiting comparatively lower extinction rates than other regions. Such spatial variation aligns with expectations for extinctions influenced by environmental factors. Palaeoclimate simulations were finally used to test whether continental shelf availability or changes in sea temperature explained extinction trends. These variables showed limited explanatory power across time, and the Pliocene extinction peak appears anomalous relative to background Neogene trends. This suggests that the drivers of the selective extinction of megafauna during the Pliocene were likely unique and multifactorial, potentially reflecting interacting climatic, tectonic, and ecological change. Overall, these findings provide new insight into an understudied extinction event, highlighting the resilience of past marine ecosystems and identifying promising directions for future research on extinction causes, mechanisms and outcomes.