Class Amphibia MOVEMENT ONTO LAND

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Class Amphibia MOVEMENT ONTO LAND
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Class Amphibia MOVEMENT ONTO LAND

• In order for animals to live on land they
• need to support their own weight (i.e., deal with
  gravity)
  
• Water more dense and also property of buoyancy
• because of this skeletal and muscular systems of
  terrestrial organisms have to be better
  developed.
  

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Class Amphibia MOVEMENT ONTO LAND

• In order for animals to live on land they
• Resist drying
• a constant problem in daily life
• rate of evaporation in most terrestrial systems
  very great
  
• resistance to drying is especially important
  during reproductive stages (i.e., egg) since they
  can not do anything actively to prevent water
  loss

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Class Amphibia MOVEMENT ONTO LAND

• In order for animals to live on land they
• deal with rapid temperature changes
• daily and seasonal changes in water environment
  less than in the air
  
• be able to extract oxygen from air
• oxygen 20 times more abundant in air than water

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Amphibian Early Evolution

• Amphibian ancestors Devonian (400 million years
  ago)
  
• Sarcopterygii (lobe-finned fishes)
• had rudimentary appendages
• had lungs - could be used used to breathe air
• during Carboniferous (350 million years ago)- was
  good environment for amphibian development
  
• characterized by wet warm environments
• lots of swampy areas
• during this time amphibians had their greatest
  rate of evolution
  

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Fish-like appendage
More like modern amphibians
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Amphibian Evolution

• Amphibians have met challenge of land only half
  way
  
• still very tied to water
• skin has to be kept wet at all times
• many use skin to aid in respiration
• all amphibians are tied to water to reproduce
• almost all lay eggs in water and larval stages
  are aquatic
  

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Amphibianscharacteristics - adults

• Upper jaw fused to skull

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Amphibianscharacteristics - adults

• with a three chambered (ventricle and two atria)

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Amphibianscharacteristics - adults

• respiration more efficient
• respiration through gills (in some), lungs, skin

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Amphibianscharacteristics - adults

• Skin
• no scales skin smooth, moist with many glands
• epidermis with keratin, below is dermis
• skin color due to chromatophores located in
  dermis

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Amphibianscharacteristics - adults

• Nervous System
• 10 pairs of cranial nerves

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AmphibiaSensory Structures
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AmphibiaReproduction

• are dioecious
• copulation is called amplexus,
• fertilization mostly external in frogs and toads
  and internal in salamanders
  
• mostly oviparous, some ovoviviparous some
  viviparous with development of larva (tadpole
  

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Amphibia AdultCharacteristics

• limbs - four (tetrapod) some are legless
• nostrils open into anterior part of mouth cavity
• many (i.e., frogs) have developed vocal chords to
  produce sounds for mating
  

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AmphibiaLarval Characteristics

• fish-like
• finned tail
• lateral line system as in fishes
• 3 pairs of gills
• 3 pairs of aortic arches
• no lungs in early stages

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Amphibia Larval Characteristics

• two chambered heart
• no limbs in early development
• some show neotony
• reach sexual maturity,
• while retaining gills and other larval
  characteristics
  
• most commonly seen in salamanders
• some are permanent "larvae"- called obligatory
  neotony (ex mud puppy- Necturus)
  

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AmphibiaSurvey of Classes

• Gymnophonia- (Apoda) caecilians
• very primitive
• up to 200 vertebrae
• limbs and girdles absent
• pantropical 160 spec

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AmphibiaSurvey of Classes

• Caudata (Urodella) salamanders
• tailed
• larvae resemble adults
• some aquatic, some fully terrestrial
• two pairs of equal limbs
• 10-60 vertebrae
• no vocal chords
• holarctic 350 species

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AmphibiaSurvey of Classes

• Anura (Salientia) frogs and toads
• larvae and adults very different
• adults tailless
• hind limbs modified for jumping
• 6-10 vertebrae
• larvae aquatic adults more terrestrial,
  especially toads
  
• no gills as adults
• have nictating membrane - prevent dessication of
  eye
  
• have vocal cords
• cosmopolitan 3400 species