Sphenolithus preasii

Sphenolithus preasii Bergen & de Kaenel in Bergen et al., 2017

This medium to large size (5.0-12.0µm) plier-like species of Sphenolithus. It is an intermediate form between Sphenolithus heteromorphus Deflandre, 1953 and Sphenolithus milanettei Maiorano & Monechi, 1998.

The fully open umbrella shape proximal cycle predominates the lateral cycle and the three-bladed monolithic looking apical spine. The segments of the small lateral cycle aligned longitudinally at 0°. The three-bladed monolithic looking apical spine is extinct (dim) at 0° and shows maximum birefringence at 45 ° in cross-polarised light.

Sphenolithus preasii differs from Sphenolithus heteromorphus and Sphenolithus milanetti by having a fully open umbrella shape proximal cycle. It is further distinguished from Sphenolithus heteromorphus by having a short lateral cycle aligned with the length of the sphenolith at 0°. The proximal cycle is a short hollow frustum shape in Sphenolithus heteromorphus whereas a semi-open umbrella shape in Sphenolithus milanetti.

Bergen, J. A., de Kaenel, E., Blair, S. A., Boesiger, T. M., Browning, E., 2017. Oligocene-Pliocene taxonomy and stratigraphy of the genus Sphenolithus in the circum North Atlantic Basin: Gulf of Mexico and ODP Leg 154. Journal of Nannoplankton Research 37(2-3), 77-112.

Deflandre, G., 1953. Hétérogénéité intrinsèque et pluralité des éleménts dans les coccolithes actuels et fossiles. Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences, Paris 237, 1785-1787.

Maiorano, P., Monechi, S., 1998. Revised correlations of early and middle Miocene calcareous nannofossil events and magnetostratigraphy from DSDP Site 563 (North Atlantic Ocean). Marine Micropaleontology 35(1989), 235-255