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Eggs and embryos from the Cambrian

S C Morris1

  • 1Department of Earth Sciences, University of Cambridge, United Kingdom. sjl11@esc.cam.ac.uk

Bioessays : News and Reviews in Molecular, Cellular and Developmental Biology
|October 22, 1998
PubMed
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Newly discovered Cambrian eggs and embryos reveal direct development in early metazoans, challenging the long-held hypothesis of ancient planktotrophic larvae and impacting our understanding of early animal evolution.

Area of Science:

  • Paleontology
  • Developmental Biology
  • Evolutionary Biology

Background:

  • The early evolution of metazoans and the nature of the Cambrian
  • explosion
  • are central questions in biology.
  • A prevailing hypothesis suggests planktotrophic larvae predated the Cambrian radiation, supported by molecular clock data.

Purpose of the Study:

  • To investigate the developmental strategies of early metazoans.
  • To re-evaluate the timing and nature of metazoan origins in light of new fossil evidence.

Main Methods:

  • Analysis of exceptionally preserved Cambrian fossils from China and Siberia (c. 530 million years ago).
  • Detailed examination of fossilized eggs, blastomeres, and embryos to reconstruct ontogeny.

Related Experiment Videos

  • Comparative analysis of developmental patterns in cnidarians and potential protostomes.

    • Main Results:

    • Discovery of Cambrian eggs with blastomeres and embryos with well-defined anatomy.
    • Evidence of direct development (no planktotrophic larval stage) in both cnidarian and protostome examples.
    • Reconstruction of ontogeny from egg to adult in tube-dwelling cnidarians.

    Conclusions:

    • The findings challenge the hypothesis that planktotrophic larvae were ancient.
    • Direct development was present in early metazoans during the Cambrian period.
    • These discoveries have significant implications for metazoan phylogeny and the interpretation of the Cambrian
    • explosion
    • .