The Early Phylogeny of Chordates and Echinoderms and the Origin of Chordate Left–Right Asymmetry and Bilateral Symmetry

  title={The Early Phylogeny of Chordates and Echinoderms and the Origin of Chordate Left–Right Asymmetry and Bilateral Symmetry},
  author={Richard P.S. Jefferies and Nigel Brown and Paul E. J. Daley},
  journal={Acta Zoologica},
Left–right asymmetry in Dexiothetica (= echinoderms + chordates) results mainly from dexiothetism—an episode in their ancestry when an animal resembling the Recent pterobranch Cephalodiscus lay right-side-downwards on the sea floor. Castericystis sprinklei belongs to the dexiothete stem group. The history of the echinoderm stem group is reconstructed. Chordate bilateral symmetry evolved by six successive steps. Tail–head overlap occurred independently in craniates and acraniates. The neural… 

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  • M. Gudo
  • Biology
    Acta biotheoretica
  • 2005
The early evolutionary history of echinoderms was reconstructed on the basis of structural-functional considerations and application of the quasi-engineering approach of ‘Konstruktions-Morphologie’ according to the presented evolutionary scenario, which resulted was an ancestral echinoderm with an enlarged metacoel.

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The Ordovician Fossil Lagynocystis pyramidalis (Barrande) and the Ancestry of Amphioxus

It follows, since Lagynocystis had a calcite skeleton, that such a skeleton has been lost at least twice in the evolution of the chordates, and that the latest common ancestor of vertebrates and amphioxus would be a primitive mitrate.

A phylogenetic test of the calcichordate scenario

The calcichordate scenario of Jefferies and colleagues purports to explain the origin and early evolution of the phyla Echinodermata and Chordata is tested, finding that it fails the erection of scenarios and fossils are unable to dictate the relationships among phyla.

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