Diversity and Disparity of Therocephalia: Macroevolutionary Patterns through Two Mass Extinctions

Henrik Richard Grunert,Jörg Fröbisch,Neil Brocklehurst

doi:10.1038/s41598-019-41628-w

Henrik Richard Grunert, Jörg Fröbisch + Show 1 more

Open Access

https://doi.org/10.1038/s41598-019-41628-w

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Abstract

Mass extinctions have the potential to substantially alter the evolutionary trends in a clade. If new regions of ecospace are made available, the clade may radiate. If, on the other hand, the clade passes through an evolutionary “bottleneck” by substantially reducing its species richness, then subsequent radiations may be restricted in the disparity they attain. Here we compare the patterns of diversity and disparity in the Therocephalia, a diverse lineage of amniotes that survived two mass extinction events. We use time calibrated phylogeny and discrete character data to assess macroevolutionary patterns. The two are coupled through the early history of therocephalians, including a radiation following the late Guadalupian extinction. Diversity becomes decoupled from disparity across the end-Permian mass extinction. The number of species decreases throughout the Early Triassic and never recovers. However, while disparity briefly decreases across the extinction boundary, it recovers and remains high until the Middle Triassic.

Highlights

Many studies have found that species richness and disparity are often not correlated[12,13,14]
All were based on the same character and taxon dataset[19] and were inferred and time calibrated using the same fossilised birth death (FBD) model under the same parameters, but different topology constraints were applied: (1) an entirely unconstrained analysis; (2) relationships constrained to those found in the parsimony analysis of Kammerer and Masyutin[19] (3) relationships constrained to those found in the parsimony analysis of Liu and Abdala[20]
It is not the purpose of this study to examine phylogenetic relationships of Therocephalia in detail, there are some differences between the topologies of the maximum clade credibility trees resulting from these analyses that warrant discussion

Summary

Introduction

Many studies have found that species richness and disparity are often not correlated[12,13,14]. As a direct result of specialization and speciation, one could expect increasing disparity early in an evolutionary history, since clades tend to diversify along ecomorphological lines in a new environment[15], leading to “early bursts” of morphological diversity independent of species richness[10,16,17]. It has been suggested that such decoupling can become more pronounced during periods of mass extinction, as if the extinction is non-selective or targets less specialised forms, disparity may remain high while diversity falls[17,18]. By quantifying three different disparity metrics, we illustrate the pattern of therocephalian evolution and extinction across the Permian-Triassic boundary

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