Trilobite diversity patterns in an Upper Cambrian stage

Abstract

Recovery of trilobite faunas following a mass extinction during the Upper Cambrian Sunwaptan Stage (equal to the “Ptychaspid Biomere”) involved increases in both within-habitat (alpha) diversity and in levels of biofacies differentiation. This pattern parallels, at a lower hierarchical level, the global increase in Phanerozoic marine invertebrate species richness (Sepkoski et al. 1981), which was influenced by changes in provinciality and in alpha diversity. Diversification slowed markedly in subtidal shelf carbonate habitats in the upper half of the stage, but continued in carbonate shelf margin environments, possibly due to higher rates of immigration from off-shelf sites. Trilobite clades appearing early in the stage have low centers of gravity, reflecting high immigration rates during and shortly after an interval of mass extinction. Expansion of shallow-water carbonate deposition in the upper half of the stage was accompanied by the spread of carbonate bank biofacies. Families occurring in these biofacies gradually increased in species richness and tended to have high centers of gravity.