Typological versus morphometric separation of orthophragminid species in single samples – a case study from Horsarrieu (upper Ypresian, SW Aquitaine, France)

Abstract

Thirteen different orthophragminid taxa could be separated typologically from a single sample collected by C.W. Drooger from the late Ypresian of Horsarrieu, marnière Sourbet (SW France). Drooger doubted the existence of many co-occurring evolutionary lineages of larger foraminifera in the Eocene suggesting that this may be an artifact of the typological species concept widely used by the Paleogene larger foraminiferal experts. It is shown here that typologically determined taxa can be separated as well with the morphometric method, recommended by Drooger. This proves also the validity of the concept of simultaneous evolutionary lineages. It has been found that the typological method is preferable when separating different taxa in single samples, but in some cases, the independence of quantitatively close populations can only be proved biometrically. At the same time, the morphometric method is more advantageous in characterizing the evolution within particular evolutionary lineages because it gives much more reliable stratigraphical results. The 13 orthophragminid taxa from Horsarrieu are systematically described. A new species, Orbitoclypeus droogeri nov. sp., and two new chronosubspecies, O. furcatus palaeofurcatus and Asterocyclina stella praestella are introduced.