A revised taxonomic and phylogenetic concept for the planktonic foraminifer species Globigerinoides ruber based on molecular and morphometric evidence

Recent SSU rDNA sequence data of the paleoceanographically important planktonic foraminifer species Globigerinoides ruber showed the presence of two distinct phylogenetic lineages within this morphotaxon. The first lineage (G. ruber sensu stricto) includes the genetic type that corresponds to pink-pigmented G. ruber, as well as three of the five genetic types recognised in individuals of “white” G. ruber (labelled Type Ia, Type Ib and Type Ib2). The remaining two genetic types of G. ruber (white), labelled as Types IIa and IIb, represent a distinct phylogenetic lineage (G. ruber sensu lato), closer related to Globigerinoides conglobatus. Here we combine molecular clock and morphometric analyses to shed light on the taxonomical and phylogenetic significance of the presence of these two distinct lineages within the morphotaxon G. ruber. A molecular clock approach suggests a rather recent origin of the G. ruber sensu stricto lineage in the late Miocene and a split between G. ruber (pink) and the “white” genotypes Ia, Ib and Ib2 around 6 Ma. This indicates that all records of G. ruber prior to the G. ruber “pseudo-extinction” event at 8 Ma refer to an unrelated species (Globigerinoides subquadratus) and that the G. ruber (pink) lineage is substantially older than the first appearance of the pink pigmentation in the fossil record. In order to establish the taxonomic identity of the G. ruber sensu lato phylogenetic lineage, we conducted morphometric measurements on (i) pictures of specimens with known genetic identity, (ii) shells from sediment samples, (iii) specimens assigned to G. ruber and Globigerinoides elongatus from a museum collection and (iv) pictures of G. ruber sensu lato morphotype from recent literature. Our results suggest that specimens of Type IIa that represent the G. ruber sensu lato lineage are morphologically identical to the concept of the G. ruber sensu lato morphotype in recent literature, and that these morphotypes are consistent with the species definition of Globigerinoides elongatus. We therefore propose that the name G. elongatus (sensu d'Orbigny) should be reinstated and used for the genetic Type IIa. The name G. ruber (sensu d'Orbigny) should be reserved for specimens of the pink chromotype. Specimens of Types Ia, Ib and Ib2 require new species names, but our data are not sufficient to provide a morphological character separating these species from their sister G. ruber (pink), other than by their shell colouration.