The influence of extinction on the rise and fall of trilobite disparity

BALSEIRO, D.; BIGNON, A.; SERRA, F

Congreso; 64th Annual Meeting of the Palaeontological Association; 2020

The Palaeontological Association

Of the many contributions of paleontology to evolutionary biology, the analysis of the evolution of morphological diversity ?i.e. disparity? is probably among the most relevant ones. In particular, the rise and fall of disparity throughout the evolutionary history of a clade has been a widely studied aspect of the fossil record. The temporal dynamics of morphological disparity are usually studied by comparing the trajectories of taxonomic and morphological diversity. However, comparing trajectories alone is not enough to understand true macroevolutionary dynamics of disparity, because it analyzes net diversification but does not individualize extinction and origination rates. In this contribution we analyze the Trilobite disparity during the Cambrian-Devonian history of the clade, integrating the largest morphometric database to date with stratigraphic ranges obtained from the Paleobiology Database. We generate time series of taxonomic and morphological diversity, extinction and origination rates, and individualize the selectivity of extinction and origination with respect to morphology using logistic regression. Net diversification is unable to explain the trend in disparity because the largest increases in trilobite morphological diversity occur at intervals of relative stable taxonomic diversity. However, studying the selectivity of extinction and origination sheds light on the dynamics underlying the trend in disparity. In particular, a modified measure of the macroevolutionary influence of extinction and origination shows how both processes complement each other to generate the observed patterns, underscoring that both extinction and origination can individually produce increases and decreases in disparity. For trilobites in particular, extinction is the main cause of morphospace expansion and contraction, pointing out that the classic idea of extinction as a constraining factor for morphological evolution is a limited view.