Chapter 24: Trilobites

ADRAIN, J.M., EDGECOMBE, G.D, FORTEY, R.A., HAMMER, O. LAURIE J., MCCORMICK, T., OWEN, A.W., WAISFELD, B.G., WEBBY, B.D., WESTROP, S.R., AND ZHOU ZHI-YI

The Great Ordovician Biodiversification Event

Columbia Universisty Press

Lugar: Chichester, Nueva York; Año: 2004; p. 231 - 245

Trilobites were a major component of the Cambrian Evolutionary Fauna and whilst overall familial and generic diversity reached a peak during the late Cambrian, one set of families, the ‘Whiterock Fauna’, showed a mid-Ordovician expansion paralleling that of clades belonging the Palaeozoic Fauna. A concomitant decline in the components of the ‘Ibex Fauna’, which had characterised the early Ordovician, resulted in an overall reduction in diversity of the Trilobita during the Period. Construction of databases and range charts for different parts of the world has enabled the complex patterns of Ordovician trilobite biodiversity change to be established and analysed. The marked biogeographical differentiation shown by trilobites in the early Ordovician and the subsequent progressive overall breakdown in provincialism, provide the global context within which their biodiversity changes are observed and interpreted. Thus, for example, within-family diversities indicate that the expansion of the Whiterock Fauna was most pronounced at low latitudes. Preliminary data also suggest that a peak in the species to genus ratio within Avalonia developed when that microcontinent separated from Gondwana and started to become biogeographically discrete as it moved towards lower latitudes. The end Ordovician extinction event resulted in a dramatic reduction in generic diversity and the extinction of the remaining families of the Ibex Fauna whereas despite very low alpha diversities during the Hirnantian, representatives of three quarters of the families of the Whiterock Fauna survived into the Silurian.