Earliest calcareous foraminifera

Abstract

WE present here evidence that early Palaeozoic calcareous foraminifera existed and were relatively complex (multilocular and multiserial) in form but that they have been regarded formerly as calcareous algae. The early part of the invertebrate fossil record during the Cambrian period seems to show a striking contrast between the abundance of highly developed organisms such as the trilobite arthropods and the paucity of simpler forms such as the foraminiferal protozoans. Foraminifera are very small acellular animals with an important role in marine food chains1 and it is reasonable to expect them to have been a significant component of the benthic fauna throughout the Palaeozoic. Yet few foraminifera have been reported from the Lower Palaeozoic and those described from the Cambrian are mainly simple forms with unmineralised tectinous or agglutinated tests2–4. Some more complex agglutinated forms are known from the Upper Cambrian5, but the first generally recognised calcareous foraminifer is the uniserial Saccaminopsis from the late Ordovician4. Consequently, the assumptions that Lower Palaeozoic foraminifera were primitive and mainly non-calcareous have been taken as bases for inferences concerning the early evolution of the group3–4 and the paradoxical, yet apparently inescapable, conclusion has been drawn that Cambrian foraminifera are very scarce.