Paleontology #04
Chapters 4, 7.

SHARKLIKE FISHES
(Class CHONDRICHTHYES)

The sharklike fishes (Chondrichthyes) are a very successful group of marine predators.
Their flexible skin is covered with tiny denticles (placoid scales); true bone is otherwise absent, and the skeleton remains cartilaginous throughout life.
Most sharks (Selachii) have a hyoid arch that helps push the jaws forward and enlarge the gape, but ratfishes (Holocephali) have the upper jaw fused to the skull.

  • Successful swimming adaptations
  • Hyoid arch
  • The classes of fishes
  • Class CHONDRICHTHYES (sharklike fishes)
    1. Cartilaginous skeleton
    2. Placoid scales
    3. Almost always marine (except for Xenacanthus)
    4. Never any lungs
    5. Male "claspers" derived from pelvic fin
  • Subclass Selachii, with amphistylic or hyostylic jaw suspension, no operculum
    • Cladoselachii
    • Pleuracanthida (Xenacanthida)
    • Selachii:  pre-Triassic / Hybodontidae / modern
    • Batoidea (skates and rays)
  • Subclass Holocephali:  Chimaeras ("rat-fishes"), with autostylic jaw suspension, operculum
    Illustrations

  • Early Paleozoic geology and vertebrate faunas
    • Burgess shale
    • Early Paleozoic environments and their faunas

Syllabus
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