SUBSTRATE RELATIONSHIP GUIDED MOLLUSCAN BODY-SIZE RESPONSE TO CLIMATIC FLUCTUATION DURING THE PAST 66 MA
Mean body-size and temperature estimates appear to track each other negatively when binned by geologic stages; however, it is not observable when the mean body-size and temperature time series are detrended by a first-differences transformation implying a lack of size-reduction due to climatic warming during Cenozoic. There exists a strong negative correlation between maximum body-size and ρ1st (size-temp) (the coefficient of correlation between 1st difference of mean body-size vs temperature) for infaunal families implying that families with smaller body-size tend to show higher magnitude of change with climatic fluctuation compared to bigger ones. Epifaunal families do not show such “existing size dependence”. A significant negative correlation for infaunal families also exists between ρ1st (size-temp) and latitudinal range implying that families with limited latitudinal range show higher magnitude of body-size change compared to widespread taxa. Such “latitudinal range dependence” is absent among epifaunal families. This difference in response between infauna and epifauna is due to the dissimilar thermal-sensitivity of these groups evolved due to their non-uniform exposure to thermal fluctuation. Our results highlight the dependence of climate induced morphological response on ecological character indicating the complexity in generalizing the biotic outcome of future climatic fluctuation.