Heterostegina matteuccii sp. nov. (Foraminiferida: Nummulitidae) from the lower Oligocene of Sicily and Aquitaine: a possible transatlantic immigrant

The systematics and phylogenetic relations of the Oligocene species of Heterostegina (Nummulitidae) are poorly known compared to those of Eocene and Miocene species. The new species Heterostegina matteuccii sp. nov., characterized by the combination of an advanced nepionic stage (i.e. very few operculine chambers) and a relatively small proloculus, is here described from the lower Oligocene Caltavuturo Formation of Portella Colla (Madonie Mts, Sicily, Italy). The same species is recorded also in the ‘Calcaire à astéries’ Formation of Illats (Northern Aquitaine, near Bordeaux, France). Biometrically, H. matteuccii sp. nov. does not fit within any known Neo-Tethyan lineage of Heterostegina from the Eocene to the Miocene, and hence is considered to be a member of a distinct phyletic lineage. The advanced nepionic stage of H. matteuccii sp. nov., however, calls for the existence of predecessors. The Priabonian (and possibly also earliest Oligocene) H. ocalana Cushman, 1921 from the American-Caribbean realm is here interpreted as the most probable ancestral form for the H. matteuccii lineage. Thus, an early Oligocene eastward transatlantic migration of this lineage may be inferred. New results of strontium isotope stratigraphy from both sides of the Atlantic Ocean are consistent with this hypothesis.