A sea of Lilliputians

Smaller size is generally seen as a negative response of organisms to stressful environmental conditions, associated with low diversity and species dominance. The mean size of the coccolithophorids decreased through the Neogene, leading to the prediction that their extant representatives are characterized by poor diversification and low specialization. The study of the (exo)coccospheres of selected taxa in the order Syracosphaerales negates this prediction, revealing that on the contrary some living lineages are highly diversified and remarkably specialized. Whereas the general role of coccoliths remains indeterminate, this analysis suggests that some may be modified for the collection of food particles, including picoplankton, thus implying that mixotrophy may characterize these lineages. In the living coccolithophorids, species richness of genera is inversely correlated with the size of cells (2 µm to 36 µm), definitive evidence that small size is part of a morphologic strategy rather than a sign of evolutionary failure. Because of their extreme minuteness, the living nannoplankton can be well compared to Lilliputians, but the trend toward size decrease in Neogene lineages is not attributable to the Lilliput effect described by Urbanek (1993).