L8:The Radiation of Chondricthyes, the Cartilaginous fish: sharks, rays and ratfish

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  • The Radiation of Chondricthyes, the Cartilaginous fish: sharks, rays and ratfish
    • Tesserate Calcified cartilage
    • Pelvic Claspers in males
      • Jawed vertebrates used to all have them
      • Modified appendages- used as intromittent organs for sperm transfer
      • Support by cartilaginous radials (rays) inside pelvic fins
      • Specialised muscles allow the clasper to be re-orientated and to pump sperm
    • Anterior Frontanelle on the skull
      • AKA precerebral fenestra OR rostral fenestra
      • Excavation on the top surface of the braincase
      • Results as a lack of calcification
      • Variable in shape and orientation
      • Skull lighter.... but other functions unknown
    • Placoid Scales
      • Skin denticles except some chimaeras and have different shapes
      • Unique perichondral pattern and no extensive overlap
      • Calcification (mineral deposition occurs around cartilaginous elements)
      • Confers strength and rigidity to the skeletal elements (skeleton remains light though) so is an adaptation to fast swimming and enhanced manoeuvrability
      • Cap of enamel-like substance; underlying bony base embedded in the dermis of the skin
      • Stop growing after a while, and increase in number with age
    • Experienced bone loss
  • Two rays joined together w/ an internal canal formed (excavation)
  • SHARKS
    • Generally fusiform bodies
    • Ventral subterminal mouths
    • Large rostrum ('nose' skeleton)
    • Teeth w/ enlarged bases
    • Jaw suspension via hyomandibula and flexible anterior ligament
    • Paired occipital condyles
    • Strongly calcified vertebrae
  • RAYS
    • Flattened bodies
    • Enlarged pectoral fins fused to head
    • Ventral gill slits and mouth
    • No anal fin
    • Eyes and spiracles on top of head
    • Hyomandibular jaw suspension
    • Highly protrusible upper jaw
  • CHIMAERAS / RATFISH
    • Heterocercal whip-like tail
    • Operculum
    • Teeth shaped like crushing plates
    • Presence of tenacula (extensions of unknown function) on their rostrum
    • Occasional presence of poison gland associated with a dorsal spine
    • Autostylic jaw suspension (upper jaw fused to skull)
    • NO spiracle

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