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The Evolution of fishes

The Evolution of fishes. Add paired appendages Better tail (symmetrical) Add jaws Loose the armor Strengthen internal skeleton. How to become a better fish. Adding jaws Clearly from gills Mouth lined with ectoderm Movement of markers: nasal opening, Why jaws= value?

cassidy-shelton
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The Evolution of fishes

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  1. The Evolution of fishes

  2. Add paired appendages Better tail (symmetrical) Add jaws Loose the armor Strengthen internal skeleton How to become a better fish

  3. Adding jaws • Clearly from gills • Mouth lined with ectoderm • Movement of markers: nasal opening, • Why jaws= value? • How can you get rid of a gill if gills are useful? = structural improvement • Note: teeth over much of mouth = ectoderm, same structure as dermal armor = bone, dentine, enamel.

  4. Jaw types and jaw structure primitively; cartilagenous inner structure = gill bar Outer structure = dermal armor

  5. Paired appendages 1. Why? – stabilize swimming 2. some primitive forms with fin fold

  6. Acanthodians = primitive bony fish with spines for fins, more than 2 pair primitively.

  7. Advanced fish – 2 pairs of fins (why two?? Functions?) Ray fin structures – found in all sharks, skates, rays.

  8. Bony fish skeletons Actinopterygians = ray fins Note change in position of pelvic Fin pair. Why??

  9. Crossopterygian or sarcopterygian: bony fish with a fleshy fin = central bone elements and muscle with a ray fringe.

  10. Note fleshy fin types: Symmetrical = lungfish Assymetrical = crossopterygians (extinct) And coelacanth – marine living

  11. Primitive: heterocercal tail Advanced bony fish = homocercal = symmetric

  12. Placoderms Head and shoulder armor

  13. Primitive bony fish = Amia fairly solid outer skull. Advanced bony fish Skull reduced to barin case, jaw and gill supports – no heavy outer armor.

  14. Fish scales Primitive = ganoid = bone and enamel form a tile mosaic- solid. Placoid = similar but isolated in sharks Cycloid, ctenoid = reduced = thin, light weight.

  15. Material of the internal skeleton Old view – since cartilage replaced by bone, cart fish are older, gave rise to bony fish New view – Placoderms, with external bony armor and internal cartilage, arise from Agnatha – Both bony and cartilagenous fish arise from placoderms

  16. So: make sense out of it for classification • How to strengthen skeleton and lighten skeleton • bony fish = osteichthyes – turn internal cartilagenous skeleton into bone for greater strength, and lighten external armor • cartilagenous fish = chondrichthyes – keep internal cartilagenous skeleton, but add some calcium salt, turn external armor into ‘denticles’ = tooth like scales • note; teeth = denticles in mouth. • So • Placoderms = armored = ancestral

  17. Notochord – jelly filled, hydrostatic skeleton

  18. Chondrocytes Matrix of collagen cartilage

  19. Haversian system Haversian canal Osteocyte (lacunae, space where cell is) Canaliculi Matrix is hydroxyapatite + collagen Typical bone

  20. Origin of bone by replacement of cartilage

  21. Origin of intermembranous bone = direct ossification in tissue, no cartilage precursor

  22. Fish- placoid scale Enamel on outside = solid Dentine inside = has canals Bone at base = canals and cells

  23. Chondrichthyes sharks, skates, rays and ratfish (Chimaera) Ratfish weird = no scales, mollusc eaters, deep sea, not too closely related

  24. Bony fish Four fin types: ray fin spine fin flesh fin – symmetrical flesh fin - assymetrical

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