1. Origin of vertebrates And the evolution of “fish”
The Deuterostomes
Origin of vertebrates
And the evolution of “fish”

2. Chordates (including vertebrates) and Echinoderms

3. Basic deuterostome characteristics
(vs Protostome)
Radial vs spiral clevage
Mesoderm formation
2nd opening into gastrula = mouth
not first

6. Echinoderm variation

8. Sea lilies; marine, sessile, filter feeders, external sieves.

9. The Chordates Have a dorsal nerve cord (sometime)
Have a notochord = dorsal stiffening rod retained in adult vertebrates as organizer for dorsal nerve cord
Have gills or pharyngeal clefts
All three features are organizers for later development – so are retained in embryos.

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

12. Vertebrates – a subset of chordates with a vertebral column.
Agnatha – most primitive vertebrates:
vertebrates: have notochord, dorsal nerve cord, gills
primitive: no jaws, no paired appendages, 2 semicircular canals
in ear.
Agnatha: living = lamprey, hagfish,
Scavengers and parasites.

13. Fossil Agnatha: add bony armor; filter feeding.

17. Non-vertebrate Chordates.
Amphioxus

18. No limbs, no jaws, gills a feeding device (become respiratory when armor added and skin respiration no longer possible. Also size increase means need something more than skin for respiration), but has a notochord, nerve cord and gills. Marine organisms.

19. Another non-vertebrate Chordate.
Tunicate

20. Adult: filter feeder – basket of “gills”
No nerve cord, no notochord, mostly eats and reproduces.
Larvae – some have motile larvae = dispersal and ability to choose substrate.

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

22. Somatic organism = nerves, brain, muscle, tail,segmentation, notochord –voluntary nervous system = swimming portion of larva
Visceral organism = gut, reproduction, respiration = involuntary nervous system = adult portion of larva

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

24. Agnatha (fossil ones)
Armored – heavy
Tail asymmetric
no jaws
Not much paired appendages
Internal skeleton of cartilage
Sea scorpion; arthropod, up to 6 feet long. predatory

25. How to become a better fish
Add paired appendages
Add jaws
Loose the armor
Strengthen internal skeleton

26. Jawless fish
Armored fish
Cartilaginous fish
Spine fins
Bony fish

27. Paired fins allow stabilization and maneuverability.

28. Fin types Fin fold Spiny fin Ray fin Fleshy fin
Ray fin fleshy fin, fleshy fin
symmetrical asymmetrical

29. Agnatha with fin folds

31. Shark with ray fin

32. Turn gills into jaws: what permits this?
Gills become more efficient, not as many needed.
Primitive fish – 7 gills, modern fish 3.5
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33. Class placodermi ; added jaws but still has armor on head and shoulders.

35. shark skin = denticles = small teeth, = same structure as dermal armor of primitive fish and of our teeth – enamel on outside, dentine underneath, then bone.

37. Class Osteichthyes
Turn internal cartilage into bone during development
Reduce armor to thin scales.

38. Note: dual origin of skelton
Blue and red = internal skeleton
Cartilage (blue) being replaced by bone (red)
Pink – the skull is direct ossification, no cartilage precursor and is remnant of old dermal armor, protecting head and brain.

39. Crossopterygian; sarcopterygian with fleshy fin