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A molecular timescale for vertebrate evolution

S Kumar1, S B Hedges

  • 1Department of Biology and Institute of Molecular Evolutionary Genetics, Pennsylvania State University, University Park 16802, USA.

Nature
|May 15, 1998
PubMed
Summary
This summary is machine-generated.

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BMC evolutionary biology·2001

Estimating evolutionary divergence times using molecular data from 658 nuclear genes reveals new insights into vertebrate and mammal evolution. This molecular clock approach challenges existing fossil records, suggesting earlier diversification than previously thought.

Area of Science:

  • Evolutionary Biology
  • Molecular Phylogenetics
  • Paleontology

Background:

  • Establishing evolutionary timescales is crucial for understanding macroevolutionary patterns and biogeography.
  • Traditional divergence time estimates rely on the fossil record, which can be incomplete.
  • Molecular clock methods offer an alternative, but historically limited by the number of available genes.

Purpose of the Study:

  • To provide robust divergence-time estimates for mammalian orders and major vertebrate lineages.
  • To compare molecular-based divergence times with existing fossil records.
  • To identify potential gaps in the Mesozoic fossil record.

Main Methods:

  • Analysis of 658 nuclear genes to estimate molecular divergence times.
  • Comparison of molecular clock estimates with fossil-based divergence times across different geological eras.

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Main Results:

  • Molecular divergence times align with early (Paleozoic) and late (Cenozoic) fossil-based estimates.
  • Significant discrepancies suggest major gaps in the Mesozoic fossil record.
  • At least five placental mammal lineages originated over 100 million years ago.
  • Most modern mammalian orders likely diversified before the Cretaceous/Tertiary extinction event.

Conclusions:

  • Molecular data provide a powerful tool for refining evolutionary timescales, especially where the fossil record is sparse.
  • The study highlights the early diversification of mammals, predating the end-Cretaceous extinction.
  • These findings necessitate a re-evaluation of the completeness of the Mesozoic fossil record for understanding mammalian evolution.