Controlling for the species-area effect supports constrained long-term Mesozoic terrestrial vertebrate diversification

Roger A Close,Roger B.J Benson,Paul Upchurch,Richard J Butler

doi:10.1038/ncomms15381

Abstract

Variation in the geographic spread of fossil localities strongly biases inferences about the evolution of biodiversity, due to the ubiquitous scaling of species richness with area. This obscures answers to key questions, such as how tetrapods attained their tremendous extant diversity. Here, we address this problem by applying sampling standardization methods to spatial regions of equal size, within a global Mesozoic-early Palaeogene data set of non-flying terrestrial tetrapods. We recover no significant increase in species richness between the Late Triassic and the Cretaceous/Palaeogene (K/Pg) boundary, strongly supporting bounded diversification in Mesozoic tetrapods. An abrupt tripling of richness in the earliest Palaeogene suggests that this diversity equilibrium was reset following the K/Pg extinction. Spatial heterogeneity in sampling is among the most important biases of fossil data, but has often been overlooked. Our results indicate that controlling for variance in geographic spread in the fossil record significantly impacts inferred patterns of diversity through time.

Highlights

Variation in the geographic spread of fossil localities strongly biases inferences about the evolution of biodiversity, due to the ubiquitous scaling of species richness with area
Ecological limits predict that regional diversity should follow a logistic curve, eventually reaching a dynamic equilibrium analogous to that described by MacArthur and Wilson’s16 model of island biogeography[17,18]
If ecological limits regulate diversification rates in deep time, terrestrial diversity may have been broadly comparable to present-day levels for much of its history, or undergone long-term equilibrial periods punctuated by abrupt increases caused by major environmental perturbations or the evolutionary origins of key innovations[8,15,19,20]

Summary

Introduction

Variation in the geographic spread of fossil localities strongly biases inferences about the evolution of biodiversity, due to the ubiquitous scaling of species richness with area. This obscures answers to key questions, such as how tetrapods attained their tremendous extant diversity. Most disagreement surrounds the degree to which ecological limits constrain patterns of diversification on continental scales[9,10,11,12,13,14] This question has profound implications for our understanding of past, present and future biodiversity. Time series of species richness inferred from the fossil record are a critical line of evidence for distinguishing bounded versus unbounded diversification over geological timescales[23,24]. This is important, because species-area relationships are ubiquitous[16,31], and the geographical area accessible to palaeontologists ( 1⁄4 palaeogeographic spread) varies dramatically among intervals of deep time[8,25,29,32,33,34]

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Results

Conclusion