The oldest vertebrates had outer skeletons made of plates of dentine. In later vertebrates, a layer of enamel covered the plates; their external armor consisted of "teeth." On some animals, the "teeth" fused into large shield plates that covered most of the body.

Sharks: jawed vertebrates with cartilaginous skeletons, including Cladoselache, skates, and rays
New features:

  • Denticles skin-teeth have a pulp cavity surrounded by layers of dentine and enamel
  • Unique pattern of tooth replacement rows of teeth in jaws are continuously replaced
  • Claspers extend from the male's pelvic fins to transfer sperm to the female during mating
Transcript of Panel Text and Description of its Pictures Follows
When? 380 million years ago to present

Skin-teeth in modern sharks:

  • Toughen the skin; a feature that's especially useful for bottom-dwellers that scrape along the ocean floor
  • Streamline the skin. Tiny ridges on skin-teeth speed water flow over the body.
  • Protect against predators and external parasites.

Skin-teeth in ancient vertebrates:

  • Protected against predators and external parasites
  • May have detected physical or chemical changes in the water (exposed dentine is very sensitive -- think of a toothache!)

PICTURE CAPTIONS:
  • Diagram showing common ancestry and evolution of sharks, placoderms, and lunged vertebrates from organisms with jaws and stomach.
    3-D TOUCH SAMPLES:
  • shark skin
    Notorynchus cepedianus (recent specimen)
    Pacific Ocean
  • placoderm
    Bothriolepis canadensis (cast of fossil)
    370 million years ago; Quebec

Learn more about how today's Great White Sharks are related to the earliest shark species (White Death).

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