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Convergent Evolution01:54

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Updated: Nov 26, 2025

Dissection and Flat-mounting of the Threespine Stickleback Branchial Skeleton
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Vertebrate Evolution: Jawless Heads Go with the Flow.

Zerina Johanson1

  • 1Department of Earth Sciences, Natural History Museum, London, UK.

Current Biology : CB
|December 8, 2020
PubMed
Summary

Palaeozoic jawless vertebrates, despite heavy armor, were active swimmers, not bottom feeders. This finding reshapes our understanding of early vertebrate evolution and the transition to jawed species.

Area of Science:

  • Paleontology
  • Functional Morphology
  • Evolutionary Biology

Background:

  • Palaeozoic jawless vertebrates (Agnatha) are crucial for understanding vertebrate evolution.
  • Previous research suggested these early vertebrates were primarily sedentary bottom-dwellers.
  • Their heavy bony armor was thought to impede active swimming.

Purpose of the Study:

  • To re-evaluate the locomotion capabilities of Palaeozoic jawless vertebrates.
  • To test the hypothesis that these ancient animals were active swimmers.
  • To understand the functional implications of their armor on swimming.

Main Methods:

  • Advanced hydrodynamic analyses were employed.
  • Biomechanical modeling was used to simulate swimming performance.

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  • Fossil data on body shape and armor were integrated.

    • Main Results:

    • New hydrodynamic analyses reveal Palaeozoic jawless vertebrates were capable swimmers.
    • The heavy bony armor did not prevent active, agile movement in the water column.
    • Results contradict prior assumptions of a purely benthic lifestyle.

    Conclusions:

    • Palaeozoic jawless vertebrates were likely active swimmers, challenging long-held hypotheses.
    • This finding significantly impacts our understanding of early vertebrate evolution.
    • The study provides new insights into the transition from jawless to jawed vertebrates.