Dating the Time of Origin of Major Clades: Molecular Clocks and the Fossil Record

2002 ◽  
Vol 30 (1) ◽  
pp. 65-88 ◽  
Author(s):  
Andrew B. Smith ◽  
Kevin J. Peterson
Keyword(s):  
Fossil Record ◽  
Molecular Clocks ◽  
Time Of Origin

scholarly journals Survival and selection biases in early animal evolution and a source of systematic overestimation in molecular clocks

2019 ◽  
Author(s):  
Graham Budd ◽  
Richard P. Mann
Keyword(s):  
Fossil Record ◽  
Null Hypothesis ◽  
Cambrian Explosion ◽  
Molecular Clocks ◽  
Statistical Structure ◽  
Animal Evolution ◽  
Evolutionary Radiation ◽  
Large Groups ◽  
Time Of Origin ◽  
Looking Back

Important evolutionary events such as the Cambrian Explosion have inspired many attempts at explanation: why do they happen when they do? What shapes them, and why do they eventually come to an end? However, much less attention has been paid to the idea of a “null hypothesis” – that certain features of such diversifications arise simply through their statistical structure. Looking back from our own perspective to the origins of large groups such as the arthropods, or even the animals themselves, will expose features that look causal but are in fact inevitable. Here we review these features with particular regard to the Cambrian explosion. We conclude that the fossil record of the late Ediacaran to Cambrian is very likely to be recording a true evolutionary radiation at this time; and show how the unusually rapid nature of this event leads to characteristic over-estimation of its time of origin by molecular clock methods - an artefact that is likely to apply to other unusually fast radiations too.

scholarly journals Molecular clocks and the early evolution of metazoan nervous systems

2015 ◽  
Vol 370 (1684) ◽  
pp. 20150046 ◽  
Author(s):  
Gregory A. Wray
Keyword(s):  
Sensory Processing ◽  
Fossil Record ◽  
Sequence Data ◽  
Divergence Times ◽  
Molecular Clocks ◽  
Sense Organs ◽  
Animal Evolution ◽  
Nervous Systems ◽  
Nervous System Evolution ◽  
Fossil Records

The timing of early animal evolution remains poorly resolved, yet remains critical for understanding nervous system evolution. Methods for estimating divergence times from sequence data have improved considerably, providing a more refined understanding of key divergences. The best molecular estimates point to the origin of metazoans and bilaterians tens to hundreds of millions of years earlier than their first appearances in the fossil record. Both the molecular and fossil records are compatible, however, with the possibility of tiny, unskeletonized, low energy budget animals during the Proterozoic that had planktonic, benthic, or meiofaunal lifestyles. Such animals would likely have had relatively simple nervous systems equipped primarily to detect food, avoid inhospitable environments and locate mates. The appearance of the first macropredators during the Cambrian would have changed the selective landscape dramatically, likely driving the evolution of complex sense organs, sophisticated sensory processing systems, and diverse effector systems involved in capturing prey and avoiding predation.

scholarly journals A morphospace of planktonic marine diatoms. I. Two views of disparity through time

Paleobiology ◽  
2015 ◽  
Vol 41 (1) ◽  
pp. 45-67 ◽  
Author(s):  
Benjamin Kotrc ◽  
Andrew H. Knoll
Keyword(s):  
Molecular Phylogeny ◽  
Fossil Record ◽  
Taxonomic Diversity ◽  
Pairwise Distance ◽  
Molecular Clocks ◽  
Apparent Discrepancy ◽  
Marine Diatoms ◽  
Discrete Character ◽  
Dramatic Rise ◽  
Cretaceous Period

AbstractBoth molecular clocks and the first appearances of major groups in the fossil record suggest that most of the range of diatom morphologies observed today had evolved by the end of the Cretaceous Period. Despite this, a canonical reading of the Cenozoic fossil record suggests a dramatic rise in taxonomic diversity that can be interpreted as an explosion of morphological variety. We investigated this apparent discrepancy by using a discrete-character-based, empirical diatom morphospace, resolved by molecular phylogeny and by fossil occurrences through time. The morphospace shows little correspondence to phylogeny and little Cenozoic change in disparity as measured by mean pairwise distance. There is, however, an increase in the total volume of morphospace occupied. Although the increase in occupied volume through time ostensibly supports a conclusion of increasing morphological variety, sampling biases and other data suggest an underlying stationary pattern more consistent with molecular clock data.

scholarly journals A tardigrade in Dominican amber

2021 ◽  
Vol 288 (1960) ◽  
Author(s):  
Marc A. Mapalo ◽  
Ninon Robin ◽  
Brendon E. Boudinot ◽  
Javier Ortega-Hernández ◽  
Phillip Barden
Keyword(s):  
North America ◽  
Fossil Record ◽  
Evolutionary History ◽  
Global Distribution ◽  
Molecular Clocks ◽  
Extreme Conditions ◽  
Diverse Group ◽  
Crown Group ◽  
Dominican Amber ◽  
Terrestrial Environments

Tardigrades are a diverse group of charismatic microscopic invertebrates that are best known for their ability to survive extreme conditions. Despite their long evolutionary history and global distribution in both aquatic and terrestrial environments, the tardigrade fossil record is exceedingly sparse. Molecular clocks estimate that tardigrades diverged from other panarthropod lineages before the Cambrian, but only two definitive crown-group representatives have been described to date, both from Cretaceous fossil deposits in North America. Here, we report a third fossil tardigrade from Miocene age Dominican amber. Paradoryphoribius chronocaribbeus gen. et sp. nov. is the first unambiguous fossil representative of the diverse superfamily Isohypsibioidea, as well as the first tardigrade fossil described from the Cenozoic. We propose that the patchy tardigrade fossil record can be explained by the preferential preservation of these microinvertebrates as amber inclusions, coupled with the scarcity of fossiliferous amber deposits before the Cretaceous.

scholarly journals Survival and selection biases in early animal evolution and a source of systematic overestimation in molecular clocks

2020 ◽  
Vol 10 (4) ◽  
pp. 20190110 ◽  
Author(s):  
Graham E. Budd ◽  
Richard P. Mann
Keyword(s):  
Fossil Record ◽  
Null Hypothesis ◽  
Cambrian Explosion ◽  
Molecular Clocks ◽  
Statistical Features ◽  
Statistical Structure ◽  
Animal Evolution ◽  
Evolutionary Radiation

Important evolutionary events such as the Cambrian Explosion have inspired many attempts at explanation: why do they happen when they do? What shapes them, and why do they eventually come to an end? However, much less attention has been paid to the idea of a ‘null hypothesis’—that certain features of such diversifications arise simply through their statistical structure. Such statistical features also appear to influence our perception of the timing of these events. Here, we show in particular that study of unusually large clades leads to systematic overestimates of clade ages from some types of molecular clocks, and that the size of this effect may be enough to account for the puzzling mismatches seen between these molecular clocks and the fossil record. Our analysis of the fossil record of the late Ediacaran to Cambrian suggests that it is likely to be recording a true evolutionary radiation of the bilaterians at this time, and that explanations involving various sorts of cryptic origins for the bilaterians do not seem to be necessary.

scholarly journals Trilobite evolutionary rates constrain the duration of the Cambrian explosion

2019 ◽  
Vol 116 (10) ◽  
pp. 4394-4399 ◽  
Author(s):  
John R. Paterson ◽  
Gregory D. Edgecombe ◽  
Michael S. Y. Lee
Keyword(s):  
Fossil Record ◽  
Evolutionary Rates ◽  
Cambrian Explosion ◽  
Molecular Clocks ◽  
Genomic Evolution ◽  
Quantitative Evidence ◽  
Dating Methods ◽  
Marine Biosphere ◽  
Evolutionary Stasis ◽  
Broad Scale

Trilobites are often considered exemplary for understanding the Cambrian explosion of animal life, due to their unsurpassed diversity and abundance. These biomineralized arthropods appear abruptly in the fossil record with an established diversity, phylogenetic disparity, and provincialism at the beginning of Cambrian Series 2 (∼521 Ma), suggesting a protracted but cryptic earlier history that possibly extends into the Precambrian. However, recent analyses indicate elevated rates of phenotypic and genomic evolution for arthropods during the early Cambrian, thereby shortening the phylogenetic fuse. Furthermore, comparatively little research has been devoted to understanding the duration of the Cambrian explosion, after which normal Phanerozoic evolutionary rates were established. We test these hypotheses by applying Bayesian tip-dating methods to a comprehensive dataset of Cambrian trilobites. We show that trilobites have a Cambrian origin, as supported by the trace fossil record and molecular clocks. Surprisingly, they exhibit constant evolutionary rates across the entire Cambrian, for all aspects of the preserved phenotype: discrete, meristic, and continuous morphological traits. Our data therefore provide robust, quantitative evidence that by the time the typical Cambrian fossil record begins (∼521 Ma), the Cambrian explosion had already largely concluded. This suggests that a modern-style marine biosphere had rapidly emerged during the latest Ediacaran and earliest Cambrian (∼20 million years), followed by broad-scale evolutionary stasis throughout the remainder of the Cambrian.

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