The Shifting Balance of Diversity Among Major Marine Animal Groups

TLDR

The fossil record shows that each major taxonomic group has a consistent net diversification rate and a species‑richness limit, leading to the expectation that long‑term dominance shifts could be predicted from these traits. Recent analyses demonstrate that diversity limits can rise or fall with adaptive radiations or extinctions, occurring idiosyncratically across taxa—e.g., the end‑Permian extinction permanently reduced brachiopod and crinoid diversity—so the current crisis may permanently alter the biosphere’s taxonomic composition.

Abstract

The fossil record demonstrates that each major taxonomic group has a consistent net rate of diversification and a limit to its species richness. It has been thought that long-term changes in the dominance of major taxonomic groups can be predicted from these characteristics. However, new analyses show that diversity limits may rise or fall in response to adaptive radiations or extinctions. These changes are idiosyncratic and occur at different times in each taxa. For example, the end-Permian mass extinction permanently reduced the diversity of important, previously dominant groups such as brachiopods and crinoids. The current global crisis may therefore permanently alter the biosphere's taxonomic composition by changing the rules of evolution.