Related Experiment Video
Updated: Aug 13, 2026
10:41
Generation of Dispersed Presomitic Mesoderm Cell Cultures for Imaging of the Zebrafish Segmentation Clock in Single Cells
Published on: July 24, 2014
Estimating metazoan divergence times with a molecular clock
Kevin J Peterson1, Jessica B Lyons, Kristin S Nowak
1Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA. kevin.peterson@dartmouth.edu
Summary
The origin of bilaterally symmetrical animals is dated between 573 and 656 million years ago, aligning with fossil records. This study reveals vertebrates evolved slower molecular rates than invertebrates, impacting evolutionary timelines.
Area of Science:
- Evolutionary Biology
- Molecular Evolution
- Paleontology
Background:
- Dating the origin of bilaterians is key to understanding early animal evolution.
- Fossil records suggest bilaterians emerged around 555 million years ago (Ma).
- Molecular clock estimates, particularly for vertebrates, have yielded earlier divergence times, creating a discrepancy.
Purpose of the Study:
- To reconcile discrepancies between fossil and molecular clock estimates for bilaterian origins.
- To investigate rate differences in molecular evolution between vertebrates and invertebrates.
- To refine the estimated timeline for the emergence of the last common ancestor of bilaterians.
Main Methods:
- Comparative genomic analysis of vertebrates and invertebrates (echinoderms, bivalve molluscs).
- Utilized a concatenated data set of seven amino acid sequences from 23 taxa.
- Employed 11 invertebrate calibration points across the bilaterian tree and Phanerozoic era.
Main Results:
- Demonstrated that dipterans (invertebrates) exhibit molecular evolution rates similar to other invertebrates, unlike vertebrates.
- Showed vertebrates significantly decreased their rate of molecular evolution compared to invertebrates.
- Estimated the last common ancestor of bilaterians arose between 573 and 656 Ma, depending on rate heterogeneity parameters.
Conclusions:
- The revised molecular clock estimates align with the fossil record, supporting a bilaterian origin between 573-656 Ma.
- The Cambrian explosion likely reflects significant diversification of bilaterian phyla.
- Vertebrate genomes evolved at a slower rate than invertebrate genomes, necessitating adjustments in molecular dating.
Related Concept Videos
01:07Speciation Rates
Speciation can proceed at markedly different rates, and evolutionary biologists commonly describe these differences through the models of gradualism and punctuated equilibrium. Both patterns explain how new species arise, but they differ in the tempo and continuity of evolutionary change. In both cases, evolutionary change arises from heritable variation within populations, with natural selection often shaping traits that improve survival and reproduction under specific environmental conditions.
02:05Gene Evolution - Fast or Slow?
The genomes of eukaryotes are punctuated by long stretches of sequence which do not code for proteins or RNAs. Although some of these regions do contain crucial regulatory sequences, the vast majority of this DNA serves no known function. Typically, these regions of the genome are the ones in which the fastest change, in evolutionary terms, is observed, because there is typically little to no selection pressure acting on these regions to preserve their sequences.
In contrast, regions which code...
In contrast, regions which code...
02:54Evolutionary Relationships through Genome Comparisons
Genome comparison is one of the excellent ways to interpret the evolutionary relationships between organisms. The basic principle of genome comparison is that if two species share a common feature, it is likely encoded by the DNA sequence conserved between both species. The advent of genome sequencing technologies in the late 20th century enabled scientists to understand the concept of conservation of domains between species and helped them to deduce evolutionary relationships across diverse...
02:05Gene Evolution - Fast or Slow?
The genomes of eukaryotes are punctuated by long stretches of sequence which do not code for proteins or RNAs. Although some of these regions do contain crucial regulatory sequences, the vast majority of this DNA serves no known function. Typically, these regions of the genome are the ones in which the fastest change, in evolutionary terms, is observed, because there is typically little to no selection pressure acting on these regions to preserve their sequences.
In contrast, regions which code...
In contrast, regions which code...
01:29Modern Molecular Taxonomy
Advancements in molecular biology have revolutionized the identification and characterization of bacteria, with multiple methods leveraging DNA sequencing for enhanced precision. As sequencing technologies improve and costs decline, these approaches are increasingly used in clinical, environmental, and evolutionary studies.Multilocus Sequence Typing (MLST) examines several housekeeping genes, essential chromosomal genes encoding cellular functions, to distinguish strains. Approximately...
01:28Microbial Phylogeny
Understanding the evolutionary relationships among microorganisms is fundamental to microbial ecology and taxonomy. Phylogenetic trees are essential tools for inferring these relationships, relying primarily on comparative analyses of molecular sequences such as DNA, RNA, or proteins. In microbial studies, these trees typically depict the evolutionary paths of diverse bacterial and archaeal species by mapping genetic differences accumulated over time.Phylogenetic trees are composed of tips,...