Morphological trends in reticulate Nummulites across the Eocene–Oligocene transition

Koorapati RK, Moon BC, Cotton LJ (2025)

Publication Type: Journal article

Publication year: 2025

Journal

Palaeontology Wiley

Book Volume: 68

Article Number: e70003

Journal Issue: 2

DOI: 10.1111/pala.70003

Abstract

At the Eocene–Oligocene transition (EOT), c. 34.44–33.65 Ma, the Earth's climate shifted from ‘greenhouse’ to ‘icehouse’ conditions. This change coincides with the first continental ice growth on Antarctica, global cooling, and widespread overturning of faunal and floral assemblages. Studies have focused on the timing and mechanism of larger foraminiferal extinctions across the EOT, but there has been little work on surviving taxa. Reticulate Nummulites are a morphologically distinctive and biostratigraphically important lineage ranging from the lower Eocene to the Oligocene, surviving the climatic change. While general long-term trends across the entire lineage are well established, no previous study has examined in detail the potential of climatic events on their evolution. The Tanzania Drilling Project recovered three drill core records crossing the EOT. These are exceptionally well-constrained stratigraphically, and contain specimens of well-preserved reticulate Nummulites throughout. Using traditional oriented thin sections and micro-computed tomographic scanning, we examined the morphology of 157 individual specimens from before, during and after the EOT. Significant increases are seen in proloculus size, radii of inner whorls, and total number of whorls. Our results also show a clear expansion in morphospace across the EOT, which we interpret as a speciation event in progress linked to the climatic shift. Modelling suggests that there is a relationship between the δ¹⁸O and δ¹³C records and morphological change, indicating that factors such as temperature and nutrient cycling may play a role. However, driving mechanisms appear to vary both through time and maybe even within the growth of the foraminifera.

Authors with CRIS profile

Ravi Kiran Koorapati Lehrstuhl für Paläoumwelt

Involved external institutions

University of Bristol

United Kingdom (GB) Natural History Museum of Denmark / Statens Naturhistoriske Museum

Denmark (DK)

How to cite

APA:

Koorapati, R.K., Moon, B.C., & Cotton, L.J. (2025). Morphological trends in reticulate Nummulites across the Eocene–Oligocene transition. Palaeontology, 68(2). https://doi.org/10.1111/pala.70003

MLA:

Koorapati, Ravi Kiran, Benjamin C. Moon, and Laura J. Cotton. "Morphological trends in reticulate Nummulites across the Eocene–Oligocene transition." Palaeontology 68.2 (2025).

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