MORPHOMETRIC ANALYSES OF THE LATE NEOGENE PLANKTONIC FORAMINIFERAL LINEAGE NEOGLOBOQUADRINA-DUTERTREI

Morphometric analyses are applied to the planktonic foraminifera Neogloboquadrina acostaensis, Neogloboquadrina humerosa and Neogloboquadrina dutertrei in the Early Pliocene to Holocene interval. The distribution of four morphological variables, equatorial area, chamber number, chamber overlap and height of the trochospire, demonstrate that continuous morphologic changes characterized the evolution of the N. dutertrei lineage, therefore quantitative taxonomic differentiation of this cline into individual chronospecies is not possible. Consequently, the stratigraphic significance of the central member of the lineage, N. humerosa is reassessed, and its application as a zonal marker is discouraged. Among the morphometric variables analyzed, size tends to be the most significant indicator of the phyletic transformation from N. acostaensis, via N. humerosa to N. dutertrei and of the stratigraphic evolution of the whole lineage through time.