Tempo and mode of early animal evolution: inferences from rocks, Hox, and molecular clocks

  title={Tempo and mode of early animal evolution: inferences from rocks, Hox, and molecular clocks},
  author={Kevin J. Peterson and Mark A. McPeek and David A. D. Evans},
Abstract One of the enduring puzzles to Stephen Jay Gould about life on Earth was the cause or causes of the fantastic diversity of animals that exploded in the fossil record starting around 530 Ma—the Cambrian explosion. In this contribution, we first review recent phylogenetic and molecular clock studies that estimate dates for high-level metazoan diversifications, in particular the origin of the major lineages of the bilaterally-symmetrical animals (Bilateria) including cnidarians. We next… 

The Temporal and Environmental Context of Early Animal Evolution: Considering All the Ingredients of an "Explosion".

New analyses of sedimentary total organic carbon contents in shales suggest that the Neoproterozoic ocean may also have had lower primary productivity-or at least lower quantities of organic carbon reaching the seafloor-compared with the Phanerozoic.

The Precambrian emergence of animal life: a geobiological perspective

It is proposed that the recorded Precambrian evolution of animals includes three intervals of advancement that begin with sponge-grade organisms, and that any preceding cryptic fauna would be no more complex than sponges.

The Ediacaran emergence of bilaterians: congruence between the genetic and the geological fossil records

The two historical records of life both suggest that although the cradle of Metazoa lies in the Cryogenian, and despite the explosion of ecology that occurs in the Cambrian, it is the emergence of bilaterian taxa in the Ediacaran that sets the tempo and mode of macroevolution for the remainder of geological time.

Explaining the Cambrian "Explosion" of Animals

The Cambrian “explosion” is a unique episode in Earth history, when essentially all the animal phyla first appear in the fossil record and is best understood as being the result of the interplay of the combinatorial bilaterian developmental system and the increase in the number of needs the first bilaterians had to meet as complex ecological interactions developed.

Darwin's dilemma: the realities of the Cambrian ‘explosion’

  • S. Conway Morris
  • Geology, Geography
    Philosophical Transactions of the Royal Society B: Biological Sciences
  • 2006
It is proposed that despite its step-like function this evolutionary event is the inevitable consequence of Earth and biospheric change.

Unravelling body plan and axial evolution in the Bilateria with molecular phylogenetic markers

Key morphological transitions pose a basic difficulty: reconstruction of ancestral traits of derived clades is problematic because of a lack of transitional forms in the fossil record and obscure homologies between ‘ancestral’ and derived groups.

Darwin's dilemma: the realities of the Cambrian 'explosion'

It is proposed that despite its step-like function this evolutionary event is the inevitable consequence of Earth and biospheric change.

The earliest fossil record of the animals and its significance

  • G. Budd
  • Geography, Environmental Science
    Philosophical Transactions of the Royal Society B: Biological Sciences
  • 2008
A reasonable case can now be made for the extension of the fossil record of at least basal animals (sponges and perhaps cnidarians) to a period of time significantly before the beginning of the Cambrian.



Fossils, molecules and embryos: new perspectives on the Cambrian explosion.

The distribution of Hox and other developmental control genes among metazoans indicates that an extensive patterning system was in place prior to the Cambrian, and it is likely that much genomic repatterning occurred during the Early Cambrian.

Ideas on the timing of metazoan diversification

Fossil data suggest that the great majority of metazoan classes that existed in the Early Cambrian arose after about 700 my ago. The rectangular model of evolution, which views most evolutionary

Origin of the metazoan phyla: molecular clocks confirm paleontological estimates.

This work has analyzed 18 protein-coding gene loci and estimated that protostomes (arthropods, annelids, and mollusks) diverged from deuterostomes about 670 million years ago, and chordates from echinoderms about 600 million years old, consistent with paleontological estimates.

The Cambrian evolutionary ‘explosion’: decoupling cladogenesis from morphological disparity

Evidence is presented that the important events in the generation of clades were earlier than the Cambrian ‘explosion’, at which time the groups become manifest in the fossil record.

A critical reappraisal of the fossil record of the bilaterian phyla

  • G. BuddS. Jensen
  • Biology
    Biological reviews of the Cambridge Philosophical Society
  • 2000
It is shown that the prospect of lineage diversification occurring early in the Proterozoic can be seen to be unlikely on grounds of both parsimony and functional morphology, and this analysis points to the requirement for a careful application of systematic methodology before explanations are sought for alleged patterns of constraint and flexibility.

Bayesian models of episodic evolution support a late precambrian explosive diversification of the Metazoa.

Bayes posterior estimates of evolutionary rates indicated at least one major burst of molecular evolution at the end of the Precambrian when protostomes and deuterostomes diverged, which is broadly consistent with the fossil records.

Bilaterian origins: significance of new experimental observations.

New data on Hox gene expression patterns are discussed which suggest that both sea urchins and polychaete annelids use Hox genes in a very similar fashion, and the ancestry of the bilaterians is summarized in phylogenetic terms.

The cambrian evolutionary ‘explosion’ recalibrated

A new paradigm suggests that the ‘explosion’ in the record may have been decoupled from the evolutionary innovation, and the apparent paradox between the sudden appearance of recognisable metazoans and their extended evolutionary history might be explained by a sudden Cambrian increase in body size, which was accompanied by skeletisation.

Eggs and embryos from the Cambrian.

  • S. Morris
  • Environmental Science
    BioEssays : news and reviews in molecular, cellular and developmental biology
  • 1998
A surprising new discovery of eggs with blastomeres and embryos with well-defined anatomy from the Cambrian of China and Siberia promises to extend the arena of debate on the nature of the earliest animals and when they originated.

Estimating metazoan divergence times with a molecular clock.

The last common ancestor of bilaterians arose somewhere between 573 and 656 Ma, depending on the value assigned to the parameter scaling molecular substitution rate heterogeneity, and this results support the view that the Cambrian explosion reflects, in part, the diversification of bilateralian phyla.