Agglutinated Foraminifera: An Introduction

Unicellular protozoans are among the oldest fossils which we can recognize from the Precambrian. Presumably, foraminiferal ancestors were among the earliest of them, but had not yet benefitted from being sheltered by a biomineralized test. During the earliest Cambrian the first agglutinating foraminifera made their first appearance in the geologic record. These “primitive” forms built their test of foreign particles held together by an organic cement. This organic cement may have been secreted by the foraminifer in cytoplasmic vacuoles as is the case with Recent agglutinating foraminifera. Yet, the capability to biomineralize calcite did not evolve until after another 60 million years when the fusulinids developed their microgranular wall. Calcitic cemented agglutinates occur even later, at the base of the Carboniferous. Thus, in the fossil record the agglutinated foraminifera occur as a twofold group with a rather distinct evolution