Quantitative Approach to Diversity and Decline in Late Palaeozoic Trilobites

Abstract

Quantitative data reveal complex evolution in late trilobite diversity. In the Middle to early Late Devonian, a series of extinction events led to dramatic taxonomic impoverishment of the trilobites. In the Famennian, when only two orders remained, originations began to compensate for the still high extinction rates, marking the start of a remarkable diversification. Although interrupted by the major Hangenberg turnover, the general diversification trend accelerated in the Tournaisian, whereas extinctions became modest. Originations diminished markedly during the Viséan and Serphukovian, causing this diversity to decrease to the level observed in the Frasnian. It was never much higher thereafter, despite massive restructuring of the trilobite communities in the early Pennsylvannian; this allowed for progressive domination of the ditomopygines. After another decline in the Kasimovian, a period of stasis occurred with very low diversity levels and almost no renewal. The last burst of diversification occurred in the Wordian, but ceased rapidly in the Capitanian when degradation of environmental conditions began to inhibit originations. Thus, extinction of the Trilobita at the end of the Permian resulted from disappearance of merely a handful of genera.