RelTime Rates Collapse to a Strict Clock When Estimating the Timeline of Animal Diversification.
TLDR
This study roundly rejects a Mesoproterozoic origin of animals; metazoans emerged in the Tonian-Cryogenian, and diversified in the Ediacaran, in the immediate prelude to the routine fossilization of animals in the Cambrian associated with the emergence of readily preserved skeletons.Abstract:
Establishing an accurate timescale for the history of life is crucial to understand evolutionary processes. For this purpose, relaxed molecular clock models implemented in a Bayesian MCMC framework are generally used. However, these methods are time consuming. RelTime, a non-Bayesian method implementing a fast, ad hoc, algorithm for relative dating, was developed to overcome the computational inefficiencies of Bayesian software. RelTime was recently used to investigate the timing of origin of animals, yielding results consistent with early strict clock studies from the 1980s and 1990s, estimating metazoans to have a Mesoproterozoic origin-over a billion years ago. RelTime results are unexpected and disagree with the largest majority of modern, relaxed, Bayesian molecular clock analyses, which suggest animals originated in the Tonian-Cryogenian (less that 850 million years ago). Here, we demonstrate that RelTime-inferred divergence times for the origin of animals are spurious, a consequence of the inability of RelTime to relax the clock along the internal branches of the animal phylogeny. RelTime-inferred divergence times are comparable to strict-clock estimates because they are essentially inferred under a strict clock. Our results warn us of the danger of using ad hoc algorithms making implicit assumptions about rate changes along a tree. Our study roundly rejects a Mesoproterozoic origin of animals; metazoans emerged in the Tonian-Cryogenian, and diversified in the Ediacaran, in the immediate prelude to the routine fossilization of animals in the Cambrian associated with the emergence of readily preserved skeletons.read more
Citations
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Integrated genomic and fossil evidence illuminates life's early evolution and eukaryote origin.
Holly C. Betts,Mark N. Puttick,Mark N. Puttick,James W. Clark,Tom A. Williams,Philip C. J. Donoghue,Davide Pisani +6 more
TL;DR: The last universal common ancestor of cellular life is found to have predated the end of late heavy bombardment, and a timescale of life is derived, combining a reappraisal of the fossil material with new molecular clock analyses.
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Theoretical Foundation of the RelTime Method for Estimating Divergence Times from Variable Evolutionary Rates
TL;DR: It is shown that the basis of the RelTime approach is a relative rate framework (RRF) that combines comparisons of evolutionary rates in sister lineages with the principle of minimum rate change between evolutionary lineages and their respective descendants and will be useful for phylogenies with branch lengths derived not only from molecular data, but also morphological and biochemical traits.
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Horizontal gene transfer constrains the timing of methanogen evolution.
TL;DR: Support for methanogenesis predating the Archaean is found by analysing horizontal gene transfer events between methanogenic Archaea and Cyanobacteria, which show methanogens diverging within Euryarchaeota no later than 3.51 billion years ago.
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The Temporal and Environmental Context of Early Animal Evolution: Considering All the Ingredients of an "Explosion".
TL;DR: In this paper, the authors discuss when landmark events in early animal evolution occurred, and the environmental context of these evolutionary milestones, and how such factors may have affected ecosystems and body plans.
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The origin of animal body plans: a view from fossil evidence and the regulatory genome
TL;DR: It is assessed the emerging view that the early diversification of animals involved small organisms with diverse cell types, but largely lacking complex developmental patterning, which evolved independently in different bilaterian clades during the Cambrian Explosion.
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