Morphologic, biogeographic and ontogenetic investigation of Mid-Pliocene menardellids (planktonic foraminifera)

• Main Author: Mary, Yannick
• Other Authors: Wetzel, Andreas, Knappertsbusch, Michael W., Eynaud, Frédérique
• Format: Thesis
• Language: English
• Published: 2013
• Subjects: Dy; Indian; Pacific; Planktonic foraminifera
• Online Access: http://edoc.unibas.ch/diss/DissB_10611; https://edoc.unibas.ch/30244/; https://edoc.unibas.ch/30244/1/PhD_Yannick-Mary_2013_corrected.pdf; https://doi.org/10.5451/unibas-006194467

The definition of planktonic foraminifera species remains a major challenge, despite their central place in biostratigraphy and paleoceanography. During the last decade, combined outcomes of molecular and morphometric studies have brought to the light challenging aspects of their classification: within the formerly and traditionally defined morpho-species exists a considerable degree of genotypic variation that defines biogeographically and ecologically distinct sibling "cryptic" species. The recognition of sibling species requires techniques, which are based on other properties than the sole shell morphology. The present work investigates the morphological variability in planktonic foraminifera of the sub-genus Menardella, a subset within the genus Globorotalia, in a time slice at 3.2Ma (Mid-Pliocene). This time was selected because it includes a major diversification of menardellids, during which 6 homeomorphic species evolved, leading to an intricate taxonomy. Here, a new population-based taxonomical approach is proposed, which relies on the combination of size frequency distributions (SFDs), geometric morphometry of the shells and sequential ontogenetic reconstructions of populations. A total of 7700 specimens collected from 19 localities in the tropical Atlantic, Pacific and Indian Oceans were investigated in great detail. The collection of morphometric data was achieved with the help of an automated device, the robot AMOR. The analysis of Mid-Pliocene menardellid SFDs allowed the identification of 6 different sedimentary populations, which on the basis of morphometric and other properties - allowed the recognition of 8 distinct morphotypes.These morphotypes are differentiated by their size distribution, the shape of their test (given by the ratio of axial diameter (dY)/spiral height (dX)), their wall structure and reflectivity and their number of chambers in the final whorl. The relative abundance of these morphotypes permits the establishment of 5 distinct menardellid provinces at 3.2 Ma: morphotypes MA ...