A morphometric analysis of the primary aperture among different morphologies of “Globigerinoides”.

The Symmetry Index (SI) and the Primary Aperture Diameter Ratio (PADR) are defined in Fig 1. Dashed line indicates the best discrimination between specimens attributed to the trilobus (blue) and ruber (red) lineages, determined by linear discriminant analysis between the two groups in Zone M3. The line is perpendicular to the linear discriminant function at the position of the optimum discrimination score (z = 0). Specimens on each side of the line would be classified as belonging to either one of the groups in Zone M3.