Gradual morphological evolution in a late cretaceous deep‐sea benthic foraminiferan, Parkiella

Abstract

This study presents a detailed, quantitative account of morphological evolution in the deep‐sea benthic foraminifer Parkiella through the last 10 million years of the Cretaceous (late Campanian to Maastrichtian). Cores taken at DSDP Sites 465 and 171, in the low‐latitude central Pacific, yielded a total of 437 specimens, from 53 samples. The shape of the apical outline of the foraminifer, its chamber arrangement, shell globularity, shell area and proloculus diameter were quantified. Significant, unidirectional changes in shell morphology were observed between sampling levels, indicating that the lineage was not in a state of morphological stasis. The occurrence of morphologically intermediate paleopopulations and the generally normal distribution of morphotypes at any given sampling level suggest that the observed pattern of evolution represents an anagenetic trend in a single, non‐branching lineage. These results confirm predictions of the plus ça change evolutionary model. Gradual evolution of this lineage may represent a reaction to changed oceanographic conditions that were established after the Maastrichtian deep‐water reversal.

Keywords:

• Foraminifera
• benthic
• deep‐sea
• Cretaceous
• evolution
• Parkiella

Notes

Corresponding author; current address: Department of Geology, Royal Holloway College, University of London, Egham Hill, Egham, Surrey TW20 0EX, United Kingdom; e‐mail: [email protected]