Origin and evolution of the planktic foraminiferal Family Eoglobigerinidae Blow, 1979, during the early Danian (Paleocene)

Abstract

New evidence on the origin and diversification of the planktic foraminiferal Family Eoglobigerinidae Blow, 1979, or Paleocene spinose, cancellate lineage, has been discovered from some of the most continuous lower Danian sections known to date, especially from El Kef and Aïn Settara (Tunisia). Based on the discovery of transitional specimens, we suggest an evolution from primitive, smooth walled Palaeoglobigerina Arenillas, Arz and Náñez, 2007, to cancellate Eoglobigerina Morozova, 1959, and then on to Parasubbotina Olsson, Hemleben, Berggren and Liu, 1992, and Subbotina Brotzen and Pozaryska, 1961. The transition from Palaeoglobigerina to Eoglobigerina implied progressive textural changes in the wall surface, such as the development of pore-pits, spines and eventually a cancellate wall. This transition, however, implied minor external morphologic changes between ancestral Palaeoglobigerina fodina (Blow, 1979) and its descendant Eoglobigerina simplicissima (Blow, 1979), such as the increase in test size and the thickness of the apertural lip.