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Origin of the Vertebrates

Origin of the Vertebrates. Early recognition that this forms a related grouping, based on certain characteristics in common: internal skeleton, circulation direction, some segmentation, etc.

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Origin of the Vertebrates

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  1. Origin of the Vertebrates

  2. Early recognition that this forms a related grouping, based on certain characteristics in common: internal skeleton, circulation direction, some segmentation, etc.

  3. Agnatha (no jaw) = most primitive as no jaw, no paired appendages, and only 2 semicircular canals, not three. Considered vertebrate as it has vertebrae = segmented backbone of either cartilage (here) or bone Also, dorsal nerve cord, other features.

  4. Fossil Agnatha: no jaw, poor paired appendages, some with none, and 2 semicircular canals But: have bone as body armor and are filter feeders

  5. 2 semicircular canals in inner ear Gills for filter feeding and respiration No jaws Odd nerve area = electric sensitivity?

  6. Seeking ancestors or relationships The great split among higher animals: deuterostome or protostome

  7. Clevage pattern

  8. Other major differences • Determinate vs intedeterminate clevage • Origin of coelom (schizocoel = protostome enterocoel = deuterostome Origin of mesoderm- outpocket, vs 4d cell mesoderm skeleton(deutero) vs ectoderm skeleton (protostomes)

  9. The other major Deuterostome group = Echinoderms spiny skin, pentaradiate, etc,

  10. Fossils include sea lillies = filter feeders. Sessile. All living ones have a bilateral larvae, and are deuterostomes.

  11. Other forms related to Vertebrates Amphioxus

  12. Has segments, gills, dorsal nerve cord, also a notochord, Odd in no brain, segmented gonads, etc.

  13. Why these features? Nerve cord – coordination of movement Notochord – organizer for the nerve cord Gills – here for feeding, only later for respiration.

  14. So new group = Phylum chordata • Includes subphylum Vertebrata • Includes “odd” groups with notochord, nerve cord and gills. = amphioxus, tunicates,

  15. Tunicate

  16. Tunicate and larvae Note: origin of visceral- somatic dichotomy Visceral = adult Somatic = larval tail origin of need for dorsal nerve cord, notochord

  17. Neoteny = keep immature features into adult Paedogenesis = become an adult Earlier in life Adult = can reproduce

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