Early vertebrates and Primitive fish

What is a fish?
1. All vertebrates which aren't tetrapods
2. Aquatic vertebrate
3. (appendages - fins)
4. Gills
5. Aquatic vertebrate
  1. Paraphyletic group
6. Skin with scales of dermal region
Early vertebrates
1. Early Cambrian fossils (535mya)
  1. China - lack mineralised tissues
2. Heart and fin rays
3. Mineralised tissue - late Cambrian
CONODONTS
1. Microfossils made of Apatite: Cambrian-Triassic
  1. Similar to dentine
2. Diet: Marine algae/inverts
3. Many vertebrate characteristics
  1. (but no gill slits)
    1. Diffusion?
  2. MINERALISED TISSUE
Agnatha
1. (Jawless fish)
  1. Hagfish & Lampreys
    1. Hagfish (Myxinoidea)
      1. ~ 65 spp (all marine)
        Scavengers & predators
      2. Single nasal opening. Single semi-circular canal
      3. Degenerate eyes (skin covered)
      4. Mucoid bag
      5. Skewed sex ratios (100:1)
        Eggs with tough covering and attachment hooks
      6. Colonial/semi-colonial
    2. Lampreys (Petromyzontia)
      1. 41spp ( ~50% parasitic)
        Marine & freshwater
      2. Cartilage pipe around notochord (Arcualia)
        Simple digestive system
        Well developed kidney
        Oral gland anticoagulent
        2 semicircular canals
      3. Chloride cells gills : tidal ventilation
2. No scales
3. Eel like bodies
4. No distinct stomach, jaws or vertabrae
5. Cartilaginous
6. 5-16 pairs of gills
7. Distinct Brain
Ostracoderms
1. Anapsids
  1. relationship in flux
2. Lacked jaws - movable mouth plates
  1. filter feed / soft bodied prey
3. midline dorsal fins & some pectoral
4. Extinct: late devonian
Jawless to Jaws
1. Major evolutionary step: changes in habitat/behaviourresources
2. 1. Ancestral Agnathan: unjointed branchial arches
  1. 2. Jointed branchial arches increase ventilation
    1. 3. Mouth closing ventilatory jaws
      1. 4. Early jawed Gnathostome
        Improved locomotion, sensory and ciculatory systems
        Silurian -> mid Ordovician
        2nd Hox duplication event
        Enlarged forebrain
        Lateral line system
        4 recognised clades
3. Gnathostomata
  1. Class: Placoderms
    1. Plated skin
      1. Plates hinged
        Internal skeleton: bone & cartilage
    2. Plated teeth: Ptyctodontids
      1. Early specimens - no teeth. Later on - true teeth
    3. Primarily marine but some in estuaries and fresh water
    4. Primary benthic - dorsoventrally flattened
      1. External pelvic appendages
  2. Class: Acanthodians
    1. Many short spines and ventral fins
      1. Slender bodied
    2. Mid Ordovician
    3. Scales and heterocercal tail - primarily midwater
    4. No teeth - filter feeders
  3. Class: Condrychthyes (cartilaginous fish)
    1. Subclass: Elasmobranchii
      1. Sharks, skates, rays
    2. Subclass: Holocephali
      1. Chimaeras & ghost fish
  4. Osteichthyes (bony fish)
    1. Class: Sarcopterygii
      1. Lobe finned fish
    2. Class: Actinopterygii
      1. Ray finned fish

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Early vertebrates and Primitive fish

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