Evolution of orbitolinid foraminifers and anoxic events: A comment on an article by J. Guex, Eclogae geol. Helv. 94 (2001) 321-328

Abstract

With reference to a study by Hofker (1963) on the evolution of the Cretaceous arge foraminifer Orbitolina, Guex (1992, 2001) took the view that repeated abrupt size decreases in the deuteroconch of the embryo during overall global size and morphological complexity increase of this structural element was generated by anoxic events. However, our present knowledge on systematics, phylogeny and stratigraphical distribution of this foraminiferal group reveals that the conceptions on this matter of Hofker are largely obsolete. There are no evolutionary breaks, which can be correlated with any of the known Mid-Cretaceous anoxic events.