Diversification dynamics of total-, stem-, and crown-groups are compatible with molecular clock estimates of divergence times.

Philip C J Donoghue,Alan J S Beavan,Davide Pisani

doi:10.1126/sciadv.abf2257

Philip C J Donoghue, Alan J S Beavan + Show 1 more

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https://doi.org/10.1126/sciadv.abf2257

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Journal: Science advances	Publication Date: Jun 11, 2021
Citations: 7	License type: CC BY 4.0

Affiliation: University of Bristol

Abstract

Molecular evolutionary time scales are expected to predate the fossil evidence, but, particularly for major evolutionary radiations, they can imply extremely protracted stem lineages predating the origin of living clades, leading to claims of systematic overestimation of divergence times. We use macroevolutionary birth-death models to describe the range of total-group and crown-group ages expected under constant rates of speciation and extinction. We extend current predictions on origination times for crown- and total-groups, and extinction of stem-groups, demonstrating that there is broad variance in these predictions. Under constant rates of speciation and extinction, we show that the distribution of expected arthropod total-group ages is consistent with molecular clock estimates. The fossil record cannot be read literally, and our results preclude attempts to interpret the antiquity of clades based on the co-occurrence of stem- and crown-representatives.

Highlights

One of the principal goals of paleontology has been to establish a time scale for the tree of life [1], facilitating estimates of evolutionary rates and temporal tests of evolutionary causality
We use a mixture of simulations and mathematical derivations similar to those used by Budd and Mann [8] to relax these fixed values and explore more fully the distributions of crown-group and total-group ages that can be generated under a model of constant speciation and extinction
We explored the range of total-group ages that can be generated on the basis of constraints from phylum Arthropoda (Chelicerata + Mandibulata), the early fossil record of which is perceived to be among the best preserved, characterized, and understood of all the animal phyla [9]

Summary

Introduction

One of the principal goals of paleontology has been to establish a time scale for the tree of life [1], facilitating estimates of evolutionary rates and temporal tests of evolutionary causality. The introduction of evolutionary models incorporating rate variation across lineages and the uncertainty associated with fossil calibration [2,3,4,5] has diminished the disparity between molecular clock estimates and the fossil record, but for these iconic evolutionary radiations, a significant gap remains. Some suggest that this might be because early representatives of a clade are low in abundance, ecologically restricted, unlikely to fossilize, or are lost to the rock record [see, e.g., [6, 7]], while others claim that molecular divergence times are gross overestimates. For example, the diversification of bilaterian animals is alternately perceived to have been a Cambrian explosion based on an approximately literal reading of the fossil record versus a more protracted Precambrian diversification based on molecular divergence times [7]

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