Size variations of coccoliths in Cretaceous oceans - A result of preservation, genetics and ecology?

For explaining the recorded size patterns, three theories are discussed in detail; these include (1) preservation of nannofossils, (2) genetics and (3) paleoecology. (1) Intense dissolution or overgrowth of the nannofossils may have altered the original coccolith sizes particularly when biometric data from different sites with potentially varying states of preservation are compared. Due to its delicate morphology, Z. erectus appears most prone to dissolution, probably explaining its size pattern. (2) If the recorded size data of the remaining two species represent original patterns, these can be interpreted by new findings in recent coccolithophore genetics. It has been shown that size variations within a single cryptic species are only minor. Shifts of coccolith sizes, both in recent and fossil taxa, can be related to genotypic variation. The varying size ranges recorded for B. constans and W. barnesiae may therefore reflect diversity changes of cryptic species at the different sites. (3) These cryptic species may have preferred different depth habitats depending on geographically-controlled factors such as sea-surface temperatures, light availability or trophic load.