Comparative Analysis of the Anatomy of the Myxinoidea and the Ancestry of Early Vertebrate Lineages

• Author / Creator

  Miyashita, Tetsuto

• The question of whether a hagfish is a true vertebrate or not has profound implications about the ancestry of the clade. New anatomical evidence allows a test of their systematic position. With dissections and serial sections of original specimens, and with a literature review, a comparative analysis revealed homologues in the chondrocranium and musculature of hagfish shared with lampreys, gnathostomes, and extinct jawless vertebrates. The analysis also identified intermediate characters that foreshadow gnathostomes, including a possible precursor of the synovial joint and tendon-like pseudocartilages. However, the hierarchical organization of the homologues presented an enormous challenge to recovering a phylogenetic signal. The traditional morphological view of the vertebrate head was overturned to formulate new evolutionary models for the ancestry of vertebrates and the origin of the gnathostome jaw. A phylogenetic analysis placed hagfish more basal than other living vertebrates, and a new definition was proposed for the clade Vertebrata.

• Subjects / Keywords

  • Phylogeny
  • Lamprey
  • Origin
  • Gnathostome
  • Evolution
  • Muscles
  • Hagfish
  • Cartilage
  • Vertebrates
  • Cranial nerve
  • Neural crest
  • Chordate
  • Head
  • Cyclostome

• Graduation date

  Fall 2012

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3S65Z

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.