JTW's Evolutionary Origins - Author: Wood, John T.

Hypothesis on Vertebrate Origins Sequence

• Primitive Sessile Lophophore arm-feeder
  • Lophophorate Bryozoa: Diagram showing the detail of a single lopophore with the tentacular ring extended
  • Lophophorate Bryozoa: Diagram showing the major structures of the colonial lophophores
• Deuterostome - Protostome Divergence
  • Cleavage Differences
• Emergence of endodermal-ectodermal ciliated gill-slit at base of lophophore arms to aid in filter-feeding
  • Hemichordata Pterobranchia Rhabdopleura (diagram)
  • Hemichordata Pterobranchia Rhabdopleura: A colony of Rhabdopleura showing extended and contracted zooids
• Abandonment of Lophophore arms in favor of gill filter-feeding basket
  • Evolution of adult ancestral tunicate represents peak of adaptive effectiveness for visceral pharyngeal gill-slit filter-feeding basket
  • Urochordata Ascidiacea: Diagram showing the major internal features of a solitary ascidian adult
  • Urochordata Ascidiacea
  • Urochordata Ascidiacea: Water Flow in a Urochordate
• Emergence of free-swimming ancestral tunicate somatic larva with centralized dorsal nerve cord
  • Urochordata Ascidiacea Larvae: Diagram showing the major features of the larval stage of an ascidian
  • Urochordata Ascidiacea Larvae (diagram)
  • Urochordata Ascidiacea Larvae (photo)
  • Urochordata Ascidiacea Larvae (photo)
  • Urochordata Ascidiacea Larvae: head (photo)
  • Urochordata Ascidiacea Larvae: Diagram showing the metamorphosis of an ascidian - just after setting to the substrate
• Neoteny and retention of larval body plan by inhibition of metamorphosis - Romer's Evolutionary Scheme
  • Romer's Vertebrate Origins Schemata
  • Romer's Vertebrate Origins Morphologies
  • Urochordata Ascidiacea Larval Metamorphosis
  • Urochordata Ascidiacea Metamorphosis Towards Completion
  • Urochordata Ascidiacea Metamorphosis Towards Completion
• Emergence of cephalochordates
  • [10 Hox genes, 1 Cluster]
  • Cephalochordata Branchiostoma Larva (diagram)
  • Cephalochordata Branchiostoma (photo)
  • Cephalochordata Branchiostoma: Detail of the anterior region of the lancelet amphixous showing the nervous system, notocord, circulatory systema and the pharyngeal slits
  • Cephalochordata Branchiostoma: Cutaway Section (diagram)
  • Cephalochordata Branchiostoma: Diagram showing the cross section of a cephalochordate through the intestine posterior to the atrium
• Hox Cluster gene duplication event Emergence of vertebrates
  • 13 Hox genes, 2 - 4+ Clusters
  • Drosophila & Mouse Hox Cluster Diagram
• Emergence of neural crest by atavistic induction of vestigial metamorphic genetic program
• Emergence of Antibody Immune system via transformation of metamorphic phagocytes and Ig/CAM Superfamily
• Fusion of Hindbrain-Pharynx Complex
• Autonomic nervous system attempts domination of visceral nerve net
  • 1. Unmyelinated Parasympathetic Component - Immobilization Response
  • 2. Sympathetic Component - Mobilization Response
  • 3. Myelinated Parasympathetic Componet - Modulatory Response
• Mesodermal gill components and Vascularization
• CAMs --> Immunoglobulins
• Endostyle --> Thyroid

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