Biology 202 - Lecture 6

  1. Lecture VI.The Origin of Tetrapods, and the Amphibians
    • Origin of Tetrapods
    • Common Characteristics of Amphibians
    • Amphibian Diversity
  2. The Origin of Tetrapods
    When and how did vertebrates invade the land?
    Land vertebrates (tetrapods) probably originated in the mid Devonian, ~360mya, from sarcopterygian ancestors.
  3. Invasion of the land required several morphological andphysiological changes:
    • Skeletal System: - an axial skeleton that can support the weight of the body- limbs for support- a strong, flexible neck, including an atlas, and a lighter skull
    • Digestive System: a muscular tongue, salivary glands, and a largeintestine (colon)
    • Excretory System: N waste excreted as urea; abladder to hold both ureaand water
    • Nervous System: eyelids and tear ducts - more sensitive hearing: amiddle ear, with atympanum, columella(stapes) and oval windo
  4. Tetrapods underwent a major radiationin the early Carboniferous (~330 mya),leading to two main lineages:
    • (1) amphibians
    • (2) amniotes (reptiles, birds andmammals).
  5. Common characteristics of amphibians
    Are amphibians just “primitive” tetrapods?
    No - modern amphibians have the basic characteristics oftetrapods, plus many specializations:
  6. Integument
    • extremely important for protection,osmoregulation, temperature regulation, and respiration
    • highly vascularized, has numerous mucous glands, and lacks scales
  7. Digestive System
    most species arecarnivorous, with aprotrusible tongue
  8. Respiratory System
    • external gills in aquaticforms
    • buccal-pump (forcedpump or positive pressurepump) ventilation of lungs
    • may be supplemented orentirely replaced bycutaneous respiration
  9. Circulatory System
    • a three chamberedheart and spiralvalve enabledifferentialcontrol of bloodflow to differentbody regions
    • lymphatic systemwith lymphatic'hearts'
  10. Reproductive System
    • development is usuallyindirect, involving metamorphosis under direction ofpituitary and thyroid hormones
    • some species have direct development
    • some are paedomorphic
  11. Nervous System
    • the brain, esp. the cerebrum, is involved in more sensoryprocessing and control than in fishes
    • a special sensory patch in the inner ear detects high frequency sounds transmitted bythe columella
    • the pectoral girdle isconnected to the oval window todetect low frequency sounds
  12. Amphibian Diversity
    There are about 4200 species of amphibians,of three main types:
  13. Order Gymnophiona
    • caecilians
    • worm-like, burrowing; sensory tentacles and reduced eyes, maybe ovoviviparous
  14. Order Caudata
    • salamanders and newts
    • generalized body with four legs of ~equal length; tail presentthroughout life, internal fertilization via a spermatophore;elaborate courtship involving pheromones
    • many paedomorphic species
  15. Order Anura
    • frogs and toads
    • specialized jumpers, with long hind legs,fused tail bones, fused pelvis, short body;bifocal vision; courtship involvingvocalizations; herbivorous larvae(tadpoles)
Card Set
Biology 202 - Lecture 6
Lecture 6