Amphibians

• Water to Land Transitional Fossils

  • Tiktaalik: freshwater intermediate between lobe-finned fishes & tetrapods
  • Acanthostega: digits on forelimbs & hindlimbs
  • Ichthyostega: most land adaptations, strong vertebrae, muscles to elevate head, shoulder & hip bones, rib cage, inner ear, tail, & gills with bony elements
• Rhipidistian


  Amphibian Ancestor
• Amphibian Overview

  • Must return to water for reproduction!
  • Ontogeny = life cycle
  • Phylogeny = long term evolution
  • Quasiterrestrial = need aquatic environment to reproduce
  • Ectothermic = body temperature controlled by environment
  • Not amniotes, but still tetrapods!
  • Skeletal strengthening for bigger body support & resisting gravity pull
  • Redesigned olfactory epithelium
  • Moist habitat because of thin skin
• Caecilians

  • Derived limbless condition for burrowing in tropical forests
  • Many vertebrae in long slender body with dermal scales
  • Carnivorous
  • Blind with tentacles on head to pick up dissolved chemical cues
  • Internal fertilization, eggs with paternal care
  • Some viviparity?
• Order: Caudata

  Salamanders & Newts
• Salamander Reproduction

  1. All aquatic (red effs = transition terrestrial stage)

  2. Aquatic larval, terrestrial adult

  3. Aquatic adult, terrestrial larval [RARE]

  4. Internal fertilization with paternal egg guarding

  5. Spermatophore on ground, force female to walk over & cloaca collects

  6. Fertilized egg deposited on ground

  7. Some salamanders have direct development
• Order: Anura

  Frogs & Toads
• Decline due to chytrid fungus, ponds disappearing, UV damage in eggs
• Frog Defense


  • Jump away
  • Pretend to be dead
  • Expand lungs to look bigger
  • Aggression
• Frogs hibernate (store fat & glycogen)
• Frog Integument

  • Thin & moist
  • Stratified epithelium with keratin & spongy dermis
  • Mucus & Serous/Poison glands
• Frog Chromatophores

  • Xanthophores - yellow, orange, red
  • Iridiophores - silvery, makes colors bright
  • Melanophores - brown, black
  • Green = xanthophores + iridophores
• Frog Skeletal/Muscular

  • Short vertebral column, less flexible for transmission of hindlimb force
  • Flattened with few bones, less ossified
  • Well developed front skull, reduced posterior skull
  • 5 rayed foot & 4 rayed hand homologous to fish fins
  • Myomeres: segmented, paired muscular blocks
• Frog Respiration

  • Cutaneous during hibernation, mouth, lungs
  • Positive pressure & gulping
  • Faveoli: smallest functional lung unit
  • Voice Box = larynx with vocal cords, vocal sacs amplify sound
• Frog Circulatory

  • Closed, 3 chambered heart (1 ventricle + 2 atria)
  • Loss of gills allowed for pulmonary system to develop
  • Partial separation of blood, right atrium receives deoxygenated
• Frog Nervous

  • 3 part brain (forebrain/olfactory + midbrain/vision + hindbrain/hearing & balance)
• Frog Feeding/Digestion

  • Adults are carnivorous, larvae are herbivores
  • Extendable tongue with gland for sticky substance
  • Teeth for grasping
• Frog Sensory

  • Lateral line: pressure sensitive, help detect objects in water
  • Tympanic membrane: resembles cochlea of mammals
  • Vision (upper eyelid is fixed)
  • Lachrymal glands = moisture
  • Cornea = bend light rays, focus image
  • Retina = receive light signals & send to brain
  • Rods = dim light
  • Cones = color
• Frog Reproduction

  1. Warm breeding season

  2. Noisey males

  3. Eggs laid in moisture

  4. Amplexus: male grasps female, fertilizes eggs externally as they leave her body

  5. Zygote, blastula, gastrula, embryo with tail bud

  6. Tadpole hatches with keratinized jaws for algae & ventral adhesion disk

  7. Hindlimbs appear

  8. Tail reabsorbed, mouth transforms, lungs develop, gills reabsorbed

  9. Forelimbs appear