Agnathan brain anatomy and craniate phylogeny

Authors

  • Roman Hossein Khonsari,

    1. Centre National de la Recherche Scientifique, Institute of Neurobiology Alfred Fessard, ‘Development, Evolution and Plasticity of the Nervous System’, Research Unit 2197, Gif-sur-Yvette, France
    2. Neurobiology Unit, Scripps Institution of Oceanography and Department of Neurosciences, School of Medicine, University of California, San Diego, La Jolla, CA, USA
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  • Blaise Li,

    1. CNRS, UMR 7138, Département Systématique et Évolution, Muséum National d’Histoire Naturelle, Paris, France
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  • Philippe Vernier,

    1. Centre National de la Recherche Scientifique, Institute of Neurobiology Alfred Fessard, ‘Development, Evolution and Plasticity of the Nervous System’, Research Unit 2197, Gif-sur-Yvette, France
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  • R. Glenn Northcutt,

    1. Neurobiology Unit, Scripps Institution of Oceanography and Department of Neurosciences, School of Medicine, University of California, San Diego, La Jolla, CA, USA
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  • Philippe Janvier

    1. CNRS, UMR 5134, Département Histoire de la Terre, Muséum National d’Histoire Naturelle, Paris, France
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Roman Hossein Khonsari, Centre National de la Recherche Scientifique, Institute of Neurobiology Alfred Fessard, ‘Development, Evolution and Plasticity of the Nervous System’, Research Unit 2197, 91198 Gif-sur-Yvette, France. E-mail: bwv_1029@yahoo.fr

Abstract

The central nervous system of hagfishes displays unique characteristics that are distinct from any other craniate neuroanatomic features. Whether these hagfish characters are general for all craniates, autapomorphies of hagfishes, or merely a derived state of the general cyclostome condition is still a matter of debate that relates to the question of the monophyly or paraphyly of the cyclostomes. The present cladistic study includes 123 neuroanatomical characters of nine chordate species and supports cyclostome paraphyly, in contrast to most current molecular sequence-based phylogenies, which support cyclostome monophyly. An understanding of the unique neural characters in hagfishes is critical to inspiring further comparative and developmental studies with regards to these two conflicting results and the very deep divergence between craniates and their presumed sister groups. The recent access to hagfish developmental data may provide exciting perspectives in the understanding and characterization of the basalmost craniate node and the interpretation of hagfish brain structure.

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