TAILIEUCHUNG - The Ecology of the Cambrian Radiation - Andrey Zhuravlev - Chapter 20
CHAPTER TWENTY Calciﬁed Algae and Bacteria Calciﬁed microbes expanded rapidly in abundance and diversity from NemakitDaldynian to Tommotian. This rapid diversiﬁcation near the base of the Cambrian reﬂects a burst of cyanobacterial evolution, and commencement of an environmentally facilitated Cyanobacterial. | 20-C1099 8 10 00 2 20 PM Page 445 CHAPTER TWENTY Robert Riding Calcified Algae and Bacteria Calcified microbes expanded rapidly in abundance and diversity from Nemakit-Daldynian to Tommotian. This rapid diversification near the base of the Cambrian reflects a burst of cyanobacterial evolution and commencement of an environmentally facilitated Cyanobacterial Calcification Episode that continued into the Ordovician. No new genera appeared during the Middle-Late Cambrian and apparent diversity declined. Correlation between generic diversity and number of studies suggests that this decline might be a monographic artifact. Calcified microbes remained important components of shallow marine carbonates throughout the Cambrian. Most groups represent cyanobacteria Angusticellularia Botomaella Girvanella and Obruchevella groups or probable cyanobacteria Epiphyton Proaulopora and Renalcis groups . Chabakovia Nuia and Wetheredella are Microproblema-tica. Calcified microbes created rigid compact reef frameworks. During the Early Cambrian they were commonly associated with archaeocyaths but they continued their successful reef-building role into the Middle-Late Cambrian in the absence of a significant metazoan contribution. Distribution patterns suggest that filamentous and dendritic forms Angusticellularia Epiphyton and Girvanella groups preferred high-energy conditions and formed reefs in grainy locations whereas botryoidal forms Renalcis Group formed mudstone-associated reefs in shelf and midramp environments. There is no evidence that calcified microbes were affected by metazoan grazing disturbance or competition during the Cambrian. Conversely these microbes may have inhibited metazoan larval settlement and growth. Cambrian calcified algae are very scarce and are much less diverse than cyanobacteria. Amgaella Mejerella and Seletonella may be dasycladaleans. They are known only from the Middle Amgaella and Late Mejerella and Seletonella Cambrian of Russia and adjacent .
đang nạp các trang xem trước