CONTROLS ON MARINE INVERTEBRATE BODY SIZE CHANGES DURING THE EARLY TOARCIAN WARMING-RELATED EXTINCTION EVENT

The Pliensbachian–Toarcian interval witnessed an episode of global warming and associated environmental changes in the marine and terrestrial realm worldwide. One of the consequences of climate change was a global biotic crisis in marine ecosystems. Fossil and modern studies show that one of the most common and widespread ecological responses to global warming is a reduction in body sizes of marine organisms, which may confer a selective advantage and which may be caused by several different environmental or biotic factors. Published data show that marine mollusks underwent significant size changes during this event, including a temporary reduction in body size in some surviving taxa during the immediate post-extinction hothouse interval (i.e. the Lilliput effect). To date, such studies have, however, been based on single locations and so recorded size trends may simply reflect local depth- or facies-related changes. To address this, we undertook comparative analyses of the body sizes of fossil marine invertebrates from two separate regions (Yorkshire, UK, and northeastern Spain), collected by bulk sampling and field surveys. In northeastern Spain, significant but expected depth-related differences were found, with larger body sizes in the shallower, better-oxygenated site. While several taxa recorded the predicted reduction in body size in both regions, interspecific differences in response were recorded. Some taxa record differences in the direction or amplitude of their size change in the different localities. These results suggest that even during major global change, differences in the local environment and ecology govern the biotic responses of marine organisms resulting in site-specific and species-specific body size trends through time. Comparison of body size data with geochemical proxy data from the same sampled horizons allow us to provide a preliminary assessment of what some of these controls may been during the Toarcian.