Characteristics of Amphibians

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  • Characteristics of Amphibians
    • Major group of tetrapods (limbed verts)
    • General characteristics
      • Often with ears specialised for detecting ground or airborne vibrations
      • Often broad and abbreviated skulls with large openings and slender bones, and incompletely ossified; ossified vertebrae
      • Wet skins
      • Size varying from a little over half a centimetre to nearly two metres
      • 3-chambered hearts, ureotelic and ammoniotelic; gill and lung (and skin) breathers; four-stroke breathing mechanism
      • Ectothermic vertebrates w/ terrestrial, aquatic, arboreal and fossorial habits
      • Low metabolic rates and limited food and energy requirements
      • All amphibians possess smooth skins packed with glands, even though several species may superficially appear to have a "rough" skin
    • Glands
      • Mucous: aid in skin respiration, tbermoregulation, defense and reproduction
      • Two kinds
      • Granular: aid in defence as they secrete toxic or noxious chemical compounds
        • e.g. Parotoid glands ('next to the ear'); neurotoxin-secreting skins in lissamphibians
    • Caecilians
      • Scales embedded in skin
        • Stacks of closely packed scales lodged in connective pouches situated below the skin annulations (appearing as folds)
    • Simple skull bone configuration
      • Broad palatal vacuities delimited by palatines
      • Two condyles for neck ariculation
      • Frogs: Frontals and parietals fused into paired frontoparietals
      • Salamanders:  otic notch and tympanum lost: impedance-matching ear reduced; maxilla does not connect posteriorly with the cheek, resulting in a gap in the skull margin
      • Caecilian: otic notch and impedance matching ear lost; endochondral elements of the neurocranium fused into an os basale. bones of the jaw fuse into a pseudodentary and pseudoangular; behind the jaw articulation, a large process provides leverage for jaw-closing muscles that originate on the brachial skeleton
    • Frogs generally don't have ribs
    • Salamander generally have extremely short ribs (same with caecilians) (note: double-pronged processes of the vertebrae to which ribs articulate)
    • Four or fewer fingers in anterior limb when present
    • Levator bulbi muscle: thin, floor of orbit, innervated by 5th cranial nerve
      • Causes eye to bulge outward leading to enlarged buccal cavity (used in breathing/ feeding)
      • Frogs, salamanders and reduced form in caecilians
    • Intermaxillary gland: system of alveoli and tubules in the anterior part of the mouth (between nasal capsules)
    • Operculum-Columella complex (note circular tympanum)
      • Sits in an embayment at the back of the skull
        • Note the wide squamosal embayment for the tympanum
      • Two bones in middle ear that transmit sound to inner ear via oval window
      • Dual high/low frequency system
        • HF: >1000Hz (columella vibration-air)
          • frogs- vocalisation
        • LF: < 1000Hz (operculum and columella vibration- ground) transmitted by leg bones plus scapula (activated by opercularis muscle)
          • predator/prey detection in frogs and salamanders
      • Inner ear
        • Basilar papillae
          • hair cell system for HFs
        • Amphibian papillae
          • hair cell system for LFs
    • Green rods in retina
      • Detection of blue light, and hue discrimination in dimness


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