CAMBRIAN MULTI-CHAMBERED FORAMINIFERAL ASSOCIATIONS-IMPLICATIONS FOR EARLY COMMUNITY STRUCTURE AND FORAMINIFERAL LINEAGES

A recent discovery of a Cambrian foraminiferal assemblage in Nova Scotia reported on the earliest multichambered foraminifera. The specimens shown came from two deposits and were sparse in the original report. However new work, on the same rocks that also contained brachiopods, has discovered an abundant fauna of multichambered foraminifera in thin sections of whole rock. These specimens are extremely abundant-more abundant than if a “thin section” of modern marsh were examined-suggesting that these early forms were abundant and as we alluded to previously, represent one of the oldest intact “living fossil” assemblages. Interestingly these can be found living presently, not far from the Cambrian locality, in modern marshes of Nova Scotia. The new specimens we show illustrate the multi-chambered nature of the trochospiral, planispiral and other forms present-they are all agglutinated. It has been suggested that the foraminiferal lineage separated more than 800Ma, which allows sufficient evolutionary time for relatively complex forms to develop. This is important from an rDNA lineage standpoint because it has been also suggested previously, based on rDNA studies used to determine lineages, that Trochammina originated from the radiation of three calcareous trochospiral species. The Cambrian specimens indicate this cannot be true since the calcareous trochospiral species do not originate any earlier than late Devonian. To tackle this problem we present some new rDNA sequences obtained from several modern marsh species-Trochammina macrescens (two formae), T. inflata, Tiphotrocha comprimata and Miliammina fusca to compare with the previous sequences.