Worldwide morphological variability in Mid-Pliocene menardellid globorotalids

• The morphological diversity of Pliocene menardellid is studied in a 3.2 Ma time slice.
• We examine 19 ODP sites distributed worldwide using an automated device.
• We investigate test size and morphology to define menardellid morphotypes.
• Eight different morphotypes are recognized, showing specific biogeography.
• The morpho-species G. menardii is composed of two distinct morphotypes.

Proper species concepts of planktonic foraminifera are essential for paleo-environmental studies. Although subtle but key differences indicate the existence of sibling species, the quantitative morphological variability of foraminifera tests remains still poorly documented. We present morphological analyses of over 7500 oriented specimens of the subgenus Menardella (globorotalid foraminifera) at a time-slice at 3.2 Ma (Mid-Pliocene). Size, frequency distribution and linear test measurements were collected with an automated device, the robot AMOR. We performed morphometric investigations in a total of 19 samples distributed worldwide. Among formally established menardellid morpho-species, eight different morphotypes are recognized. The geographic variation in morphotype abundance allows for the recognition of five menardellid provinces among the tropical Atlantic, Indian and Pacific Ocean. Results suggest that during the Mid-Pliocene, the formal morpho-species Globorotalia (Menardella) menardii is in fact composed of two distinct morphotypes, which differ in size range, morphological variability and biogeography. Morphological characterization of the morpho-species Globorotalia (M.) multicamerata reveals the occurrence of three distinct morphotypes, which may represent an adaptation to their vertical distribution in the water column.