Amphibians and Reptiles

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Biological diversity - amphibians+reptiles

  • subclass Vertebrata: the tetrapods
  • fossils - Devonian
  • Sarcopterygiian fish. (Eusthenopteron)
  • Intermediate forms - some amphibian+some fish characteristics. (Tiktaalik+Livoniana)
  • Tetrapods - amphibian characteristics (Acanthostega)
  • tracks found - 400 mya - indicative - tetrapod gait+limb position 
  • limb position not splayed - digits distinct+separate
  • unlikely earliest vertebrates - very terrestrial. pelvic+pectoral girdles unable - support weight - long
  • Carboniferous (300 mya) - giant amphibians = Labyrinthodonts
  • like giant salamanders - limbs, pelvic+pectoral girdles strengthened - support weight
  • gas exchange - lungs+skin - size attainable - O2 concentration increased - Carboniferous. modern amphibian sixe limited - atmosphere O2 availability 
  • subclass vertebrata: class Amphibia
  • frogs+salamanders - 2 different groups 250 mya
  • intermediate form = frogmander - both features
  • 1st modern frog - fossil 70 mya
  • 3 orders, 7000 species
  • Anura (frogs+toads)+Caudata (newts+salamanders)+Gymnophiona (caecilians)
  • class Amphibia: order Gymnophiona
  • population - giant (1m long) caecilians - Brazil 2011
  • largest lungless vertebrates. sealed nostrils
  • muscles - jaw not seen - any vertebrates
  • Caecilians diverged - salamander-like ancestors. early 
  • fossil record poor: Eocaecilia = primitive caecilian - limb - buds
  • burrowing+aquatic lifestyles - limblessness (snakes = convergent evolution)
  • high levels - parental care
  • subclass Vertebrata: class Amphibia
  • ectothermic - temperature varies - environment 
  • most - metamorphosis. aquatic herbivourous tadpoles - carnivorous adults
  • moist permeable skin - gas exchange
  • diverse reproductive strategies+life histories increased global distribution
  • class Amphibia: order Caudata
  • newts+salamanders
  • relatively unchanged - body form - ancestral tetrapods 
  • many vertebra, reduced ribcages, long postanal tail
  • more aquatic - adults+post metamorphic juveniles: emerge onto land - feed+hibernate
  • respiratory systems = diverse
  • gills = internal (amphiuma)+external (axolotl)
  • lungs = newts need - surface (guff)
  • both = cave olms
  • neither = lungless salamanders breathe via skin 
  • neoteny/paedomorphy = retention - juvenile characteristics, adults - caudates = common
  • lungless salamanders = tiny (skin breathing limits size) suggets evolution through neotomy
  • Bolitoglossids paedomorphic features evident - feet = reduced, cartilaginous digits - suction pad
  • class Amphibia: order Anura
  • frogs+tails = more terrestrial - caudates 
  • specialised - jumping locomotion 
  • long, muscular hind legs, reduced ribcage, short vertebra, fused hip+tarsal bones, caudal bones - urostyle
  • well developed lungs - reduce dependency - skin, gas exchange - exploit dry environments
  • toads = keratinised skin cells = lower permeability 
  • Phyllomedusine tree frogs apply waxy lipid layer 
  • casque - headed frogs: ossification - skin - head
  • tree frogs…

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