The evolution of fishes
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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?

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How to become a better fish l.jpg

Add paired appendages

Better tail (symmetrical)

Add jaws

Loose the armor

Strengthen internal skeleton

How to become a better fish


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  • 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.


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Jaw types and jaw structure

primitively; cartilagenous inner structure = gill bar

Outer structure = dermal armor


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Paired appendages

1. Why? – stabilize swimming

2. some primitive forms with fin fold



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Advanced fish – more than 2 pair primitively.

2 pairs of fins (why two?? Functions?)

Ray fin structures – found in all sharks, skates, rays.


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Bony fish skeletons more than 2 pair primitively.

Actinopterygians = ray fins

Note change in position of pelvic

Fin pair. Why??


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


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Note fleshy fin types: fin = central bone elements and muscle with a ray fringe.

Symmetrical = lungfish

Assymetrical = crossopterygians (extinct)

And coelacanth – marine living


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Primitive: heterocercal tail fin = central bone elements and muscle with a ray fringe.

Advanced bony fish = homocercal = symmetric


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Placoderms fin = central bone elements and muscle with a ray fringe.

Head and shoulder armor


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Primitive bony fish = Amia fin = central bone elements and muscle with a ray fringe.

fairly solid outer skull.

Advanced bony fish

Skull reduced to barin case, jaw and gill supports – no heavy outer armor.


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Fish scales fin = central bone elements and muscle with a ray fringe.

Primitive = ganoid = bone and enamel form a tile mosaic- solid.

Placoid = similar but isolated in sharks

Cycloid, ctenoid = reduced = thin, light weight.


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Material of the internal skeleton fin = central bone elements and muscle with a ray fringe.

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


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  • So: make sense out of it for classification fin = central bone elements and muscle with a ray fringe.

  • 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


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Notochord – jelly filled, hydrostatic skeleton fin = central bone elements and muscle with a ray fringe.


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Chondrocytes fin = central bone elements and muscle with a ray fringe.

Matrix of collagen

cartilage


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Haversian system fin = central bone elements and muscle with a ray fringe.

Haversian canal

Osteocyte (lacunae, space where cell is)

Canaliculi

Matrix is hydroxyapatite + collagen

Typical bone


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Origin of bone by replacement of cartilage fin = central bone elements and muscle with a ray fringe.



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Fish- placoid scale tissue, no cartilage precursor

Enamel on outside = solid

Dentine inside = has canals

Bone at base = canals and cells


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Chondrichthyes tissue, no cartilage precursor

sharks, skates, rays and ratfish (Chimaera)

Ratfish weird = no scales, mollusc eaters, deep sea, not too closely related


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Bony fish tissue, no cartilage precursor

Four fin types: ray fin

spine fin

flesh fin – symmetrical

flesh fin - assymetrical