Phanerozoic marine biodiversity: A fresh look at data, methods, patterns and processes

Abstract

Patterns of Phanerozoic global biodiversity continue to be a major focus of palaeobiological research. Recent advances have been fuelled by the establishment of the Paleobiology Database. This new type of data compilation, based on the actual occurrences of taxa in fossil collections, has entailed the development and application of a whole set of new analytical methods. These allow to account for large-scale biases that affect estimates of palaeodiversity, in particular uneven sampling and differential preservation of rocks and fossils. The new curve of global diversity of marine genera (Alroy et al. 2008) deviates in important aspects from traditional ones. Rather than an exponential post-Palaeozoic increase in diversity, it shows an only modest rise from the mid-Palaeozoic to the Neogene. This rise is paralleled by an increase in within-assemblage (alpha) diversity. Contrasting previous conceptions, between-assemblage (beta) diversity, here presented for the first time by a Phanerozoic beta curve, does not show a long-term trend. We approximate the new global Phanerozoic marine diversity trajectory by two consecutive logistic curves, one for the Palaeozoic and one for the Mesozoic to Cenozoic. This implies two thresholds for global diversity in the Phanerozoic, although these are not far apart. We discuss the concept of a biosphere-wide carrying capacity and argue that competition for limited resources and incumbency effects are constraining the diversity of marine life on macroevolutionary scales.