Abstract
The end-Permian biotic crisis (∼252.5 Ma) represents the most severe extinction event in Earth's history. This paper investigates diversity patterns in Anomodontia, an extinct group of therapsid synapsids (‘mammal-like reptiles’), through time and in particular across this event. As herbivores and the dominant terrestrial tetrapods of their time, anomodonts play a central role in assessing the impact of the end-Permian extinction on terrestrial ecosystems. Taxonomic diversity analysis reveals that anomodonts experienced three distinct phases of diversification interrupted by the same number of extinctions, i.e. an end-Guadalupian, an end-Permian, and a mid-Triassic extinction. A positive correlation between the number of taxa and the number of formations per time interval shows that anomodont diversity is biased by the Permian-Triassic terrestrial rock record. Normalized diversity curves indicate that anomodont richness continuously declines from the Middle Permian to the Late Triassic, but also reveals all three extinction events. Taxonomic rates (origination and extinction) indicate that the end-Guadalupian and end-Permian extinctions were driven by increased rates of extinction as well as low origination rates. However, this pattern is not evident at the final decline of anomodont diversity during the Middle Triassic. Therefore, it remains unclear whether the Middle Triassic extinction represents a gradual or abrupt event that is unique to anomodonts or more common among terrestrial tetrapods. The end-Permian extinction represents the most distinct event in terms of decline in anomodont richness and turnover rates.
Highlights
The most severe extinction event in Earth’s history at the Permian-Triassic boundary (PTB;,252.5 Ma) had a major influence on the diversity of life [e.g. 1]
This study focuses on diversity patterns of Anomodontia, an extinct group of terrestrial tetrapods, throughout the Permian and Triassic periods and in particular across the end-Permian extinction event
Diversity patterns of anomodonts Anomodonts experienced three distinct extinctions during the Permian and Triassic, at the end of the Guadalupian, the end of the Permian, and close to the Anisian-Ladinian boundary. This is indicated by analysis of the raw richness data at the stage, land-vertebrate faunachrons (LVF), 5-Ma- and 1-Ma-scales, including investigations of the total richness at all scales and total richness without singletons (NTOT2NFL) and the estimated mean standing diversity (EMSD) at the 1-Ma scale only
Summary
The most severe extinction event in Earth’s history at the Permian-Triassic boundary (PTB; ,252.5 Ma) had a major influence on the diversity of life [e.g. 1]. This study focuses on diversity patterns of Anomodontia, an extinct group of terrestrial tetrapods, throughout the Permian and Triassic periods and in particular across the end-Permian extinction event. Anomodonts belong to the diverse clade of Therapsida and constituted the major primary consumers among vertebrates of their time. They play a central role for assessing the impact of the end-Permian extinction on terrestrial ecosystems. A well-documented, cosmopolitan fossil record reflects their great taxonomic and morphological diversity, ranging from small burrowing forms to large grazers, which is unparalleled by any other clade of Permian-Triassic terrestrial tetrapods [5].
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