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Chordates

Chordates. Chordates are Deuterostomes. Protostome vs. Deuterostome. Echinoderms are sister group with chordates. Bilateral symmetry Deuterostome lineage. Four Distinct Chordate Characteristics. Notochord Single tubular, dorsal nerve chord Pharyngeal pouches Post-anal tail. Notochord.

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Chordates

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  1. Chordates

  2. Chordates are Deuterostomes

  3. Protostome vs. Deuterostome

  4. Echinoderms are sister group with chordates • Bilateral symmetry • Deuterostome lineage

  5. Four Distinct Chordate Characteristics • Notochord • Single tubular, dorsal nerve chord • Pharyngeal pouches • Post-anal tail

  6. Notochord • Flexible rod-like structure • Attachment point for muscles • Often forms bony or cartilaginous vertebrae

  7. Dorsal Nerve Cord • Dorsal to alimentary canal and notochord • Forms as a tube derived from ectoderm • Anterior end thickens to form brain

  8. Pharyngeal Pouches • Openings in pharynx to outside • Early chordates – filter feeding • Evolved into gills, ear canal, parathyroid gland Eustachian tube etc…

  9. Segmentation and Postanal Tail • Segmented muscles act on notochord • Tail structure extends past anus • Swimming

  10. Subphylum UrochordataTunicates

  11. Tunicate Body Plan Adult • Sessile filter feeder • Pharyngeal slits used for capturing food in mucus • Most Chordate features not exhibited in adult form

  12. Tunicate Development

  13. Competing hypotheses • Cephalochordate hypothesis: vertebrates evolved from essentially lancelet-like ancestors • Calcichordate hypothesis: vertebrates evolved from armored bilateral echinoderms which were early chordates, distantly related to modern echinoderms.

  14. Cephalochordate hypothesis • Lancelet-like organism is the common ancestor of all vertebrates • Cephalochordate Pikaia • Rare fossils that extend back 530 million years

  15. Calcichordate hypothesis • The calcichordate hypothesis • Not widely accepted • Calcichordates • Echinoderm-like skeletons • Ambiguous chordate-like features • Chordate features may be homologous with echinoderm structures • May be too young to be direct vertebrate ancestors

  16. Calcichordate • Has both echinoderm and chordate features? • Probably a filter feeder

  17. Tunicates and Chordate Evolution • Garstang’s Hypothesis • Paedomorphosis – larval form does not develop into adult

  18. Subphylum CephalochordataAmphioxus • Free swimming filter feeder • Has all basic chordate features

  19. ConodontsEarly Chordate with some vertebrate features • Conodont teeth are very common fossils, known since early 1800s, but animal body only described in 1983

  20. Conodonts • May or may not be true vertebrates • Vertebrate characters • sense organs with capsules • CaPO4 mineralization • Non-vertebrate characters • V-shaped myomeres • notochord but no trace of vertebrae

  21. Subphylum Vertebrata • Features • Cranium – brain encased in cartilage or bone • Most have cartilage or bone endoskeleton • Complex nervous system

  22. Development of Head Structures • Derived from neural crest cells • Cells that migrate during early development and form various structures

  23. Neural Crest Migrations Facial and skull bones Lower Jaw Hyoid Heart

  24. Development of Vertebrae • Cartilage or bone surrounds notochord and nerve cord • Segmented to allow flexibility

  25. Development of Gills • Capillaries line pharyngeal slits • Increases surface area of gas exchange

  26. Development of Complex Nervous systems • Anterior brain • Anterior sense organs • Vision • Auditory • Olfactory

  27. Early Vertebrates • Agnathans • Ostracoderms • Jawless • Gnathostomes • Placoderms • Jawed

  28. Early Vertebrates

  29. Evolution of the Jaw

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