STABLE ISOTOPES AND THE PALEOBIOLOGY OF CONTUSOTRUNCANA CONTUSA AND RACEMEGUEMBELINA FRUCTICOSA
Assuming the life cycle of Cretaceous foraminifera spanned weeks to months, the lack of correlation between size and isotopic composition suggests observed variability reflects interannual differences more than ontogenetic trends. If so, efforts to determine the paleobiology of these and other extinct foraminifera based on size related isotopic trends (particularly the possible presence of photosymbionts) might be affected by strong sampling biases. Analyses of large individuals typically use fewer specimens than analyses of small individuals. Because large individuals from the same sample can have very different isotopic signatures, which individuals are selected can have a large effect on the value measured. On the other hand, the decrease in within sample variability in C. contusa up section suggests that interannual variability decreased in C. contusas habitat. If C. contusa lived in relatively deep surface waters, decreasing variability through time suggests an increasingly stratified water column in the western Atlantic through the late Maastrichtian.