OUT OF AFRICA: COMPLEX EVOLUTION OF RETICULATE NUMMULITES

Nummulites are important components of Cenozoic tropical shallow seas, reaching incredible abundances and diversity in the Eocene; however their evolution is not well understood. Reticulate Nummulites are a widespread and distinctive group within the genus Nummulites, frequently used in biostratigraphy. Studies from the Western Tethys suggest they form a single lineage, the Nummulites fabianii lineage, with an increasing proloculus size over time. This has led to their use as one of the diagnostic taxa for larger benthic foraminiferal biostratigraphy. However, outside of this region taxa that do not fit with the N. fabianii lineage have been recorded. Here we present data from European, Indonesian, Indian and East African populations spanning the Lutetian to Rupelian, which shed new light on the ancestry and relationships of these forms. These populations show significant morphological variation and are consistent with several lineages, including the newly recognised N. ptukhiani lineage which are contemporaneous but morphologically distinct from the N. fabianii lineage of the Tethys. The first occurrences of both lineages also occur within the same continent, Africa, but within different bioprovinces. The existence of multiple lineages of reticulate Nummulites indicates that their evolution is more complex than previously thought and raises questions as to whether they are monophyletic, or the result of multiple independent convergent evolutionary lineages, as well as the influence of climatic factors on their evolution. It also underlines the importance of carrying out thorough studies of larger benthic foraminifera with independent stratigraphic control from outside of the Tethyan region to more fully understand their evolution and to enable accurate biostratigraphy.