Article: Reef-associated archaeocyathans from the Lower Cambrian of Labrador and Newfoundland

The bioherms and biostromes of the Forteau Formation in southern Labrador and western Newfoundland are rich in archaeocyathans. The older bioherms contain five genera and six species while only three genera and three species are found in the younger biostromes. Metaldetes profundus, which constitutes up to 80% of the fauna in both horizons, exhibits a great variability in growth form, ranging from stick-like to cup-like to plate-like in shape. The other taxa present are ?Metaldetes simpliporus (sp. nov.), Archaeocyathus atlanticus, Archaeosycon billingsi and Arrythmocricus kobluki (gen. and sp. nov.). A new and enigmatic form Retilamina amowensis (gen. and sp. nov.) occurs as sheets and arched domes beneath which there is a diverse cavity-dwelling fauna of algae and invertebrates. The archaeocyathan fauna has many individuals yet few species. Such a distribution, in contrast to the relatively diverse fauna of other body and trace fossils associated with the bioherms and biostromes, is probably because Late Lower Cambrian time is well past the acme of archaeocyathan evolution and few genera are recorded anywhere in rocks of this age. Some aspect of the paleo-environment (probably episodic nutrient supply) was especially conducive to archaeocyathan growth, allowing them to grow in large numbers in shallow water near the shoreline.