Ediacaran origin and Ediacaran-Cambrian diversification of Metazoa

Abstract

The timescale of animal diversification has been a focus of debate over how evolutionary history should be calibrated to geologic time. Molecular clock analyses have invariably estimated a Cryogenian or Tonian origin of animals while unequivocal animal fossils first occur in the Ediacaran. However, redating of key Ediacaran biotas and the discovery of several Ediacaran crown-Metazoa prompt recalibration of molecular clock analyses. We present revised fossil calibrations and use them in molecular clock analyses estimating the timescale of metazoan evolutionary history. Integrating across uncertainties including phylogenetic relationships, clock model, and calibration strategy, we estimate Metazoa to have originated in the early Ediacaran, Eumetazoa in the middle Ediacaran, and Bilateria in the upper Ediacaran, with many crown-phyla originating across the Ediacaran-Cambrian interval or elsewise fully within the Cambrian. These results are in much closer accord with the fossil record, coinciding with marine oxygenation, but they reject a literal reading of the fossil record.

https://www.science.org/doi/10.1126/sciadv.adp7161

This would seem relevant to numerous discussions/debates on this forum, over the years.

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The idea that we have a total fossil record of the organisms that existed in the Ediacaran period is not far from claiming we could extract the total biodiversity of the Earth from what is captured in a single mudslide in Angola.

It should be a bit of an eye-opener that there are huge intervals of time entirely missing from the stratigraphic record. It’s not just that there are no, or only known organisms, in rocks of certain ages. There are geological periods from which we simply don’t have sedimentary rock that could have held fossils if the rocks existed.

Creationists are basically declaring that we are not allowed to infer that any evolution took place during such periods. It’s like claiming if you don’t know where the graves of your great-great-great-great-great grandparents are located, you can’t even infer they existed.

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