Abstract
Evolutionary timescales have mainly used fossils for calibrating molecular clocks, though fossils only really provide minimum clade age constraints. In their place, phylogenetic trees can be calibrated by precisely dated geological events that have shaped biogeography. However, tectonic episodes are protracted, their role in vicariance is rarely justified, the biogeography of living clades and their antecedents may differ, and the impact of such events is contingent on ecology. Biogeographic calibrations are no panacea for the shortcomings of fossil calibrations, but their associated uncertainties can be accommodated. We provide examples of how biogeographic calibrations based on geological data can be established for the fragmentation of the Pangaean supercontinent: (i) for the uplift of the Isthmus of Panama, (ii) the separation of New Zealand from Gondwana, and (iii) for the opening of the Atlantic Ocean. Biogeographic and fossil calibrations are complementary, not competing, approaches to constraining molecular clock analyses, providing alternative constraints on the age of clades that are vital to avoiding circularity in investigating the role of biogeographic mechanisms in shaping modern biodiversity.This article is part of the themed issue ‘Dating species divergences using rocks and clocks’.
Highlights
Establishing an evolutionary timescale for the tree of life is a focal yet elusive goal of evolutionary biology
We provide examples of how these principles might be implemented, for terrestrial lineages, in establishing biogeographic calibrations based on the uplift of the Isthmus of Panama, bridging North and South America, and two of the most widely employed biogeographic events associated with the fragmentation of the Pangean supercontinent: the separation of New Zealand from Gondwana, and the opening of the Atlantic Ocean
When inherent assumptions and attendant errors are considered, calibrations inspired by geological events are no more precise than those based on the fossil record, nor are 9 they any easier to codify
Summary
Establishing an evolutionary timescale for the tree of life is a focal yet elusive goal of evolutionary biology. The molecular clock has conventionally been employed in groups with a good fossil record to assess the efficacy of the fossil record, tectonic calibrations allow us to realize the original but forgotten aim of the molecular clock—to establish an evolutionary timescale for lineages lacking an appreciable fossil record [3] or for which no other means of direct calibration exists [30,31,32,33,34,35,36] It should come as no surprise, to discover that biogeographic calibrations have been adopted widely [27], in terrestrial groups with a poor fossil record. Accommodating these errors renders biogeographic calibrations more accurate, but often less precise
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