Comparative anatomy

• Devonian Period


  • Cycles of drought and heavy rainfall
  • Lobe-finned fish were at an advantage due to the structure of their fins
• Rise of amphibians


  • Labyrinthodon - Ancient tetrapod with complex tooth structure
  • Paraphyletic stem group
  • Restricted bony scale (restricted to abdominal)
  • Juvenile exhibit lateral line system (absent in adults)
• Acanthostega


  • Radial fin rays supporting tail fin
  • Labyrinthodont teeth
  • Lateral line system
  • Dermal skull bones, limb of digits, weight bearing girdles
  • Lacks auditory system for airborne sounds
  • Branchial arches supporting internal gills
  • Exhibit fingers & toes
• Ichthyostega


  • Vertebral column for dorsoventral flexion (unknown function)
  • Radial fin rays supporting a tail fin
  • Lateral line system & labyrinthodont teeth
  • Lobe-finned fish (sister group of tetrapods)
• Differences in the tetrapods

  • Stronger backbone
  • Muscle to support body in air & elevate head
  • Stronger shoulder & hips girdles
  • More protective rib cage
  • Modified ear to detect airborne sounds
  • Foreshortening of skull
• Amphibia - Phase 1

  • Adaptations for weight support, substrate locomotion, some terrestrial activity
• Amphibia - Phase 2


  • Adaptations for weight support and substrate locomotion and some terrest activity
• Amphibia


  • Cold blooded, ectothermic vertebrates of aquatic gilled larval stage & terrestrial adult stage
  • All possess glandular skin and lack nails/claws
  • Return to water to breed
  • Aquatic larva have gills
  • Moist skin and in respiration
  • Improved circulatory system
  • Toxic skin glands for protection
  • Sensory regions of brain processing vision, hearing, balance expanded compared to fishes
  • Locomotion - salamanders less efficient, anurans capable of hopping, jumping, become most successful group
• Order Caudata (Urodela)


  • Salamanders & newts have long bodies & tails, most have 4 limbs at right angles to body
  • Respiration can occur through salamander skin
  • Carnivores
  • Adults live in moist wood where they tunnel under rocks & rotting logs
  • Internal fertilization, female stores spermatophore deposited by male on a leaf or stick
• Red-spotted newt life cycle

  1. Aquatic larval form

  2. Metamorphoses into red eft which remains on land for 1-3 years

  3. Then becomes secondary aquatic adult newt
• Some salamander and Proteidae species exhibit paedomorphosis - retain gills throughout life cycle
• Order Anura


  • Without tail
  • Frog & toad have long, powerful rear legs to leap long distances
  • Chunky body, bulging eyes, long sticky tongue used to catch prey
  • Lay eggs, young spend part of life as tadpoles
• Order Anura


  • Frogs: long legs, smooth skin, slender

  Toads: short legs, warty skin, live far away from water
• Order Apoda (Caecilians)


  • Limbless except for some aquatic species
  • Live in burrows in damp locations
  • Cylindrical bodies with annular rings
  • Typically range in length from 90-1600mm
  • Integument is vascular, adapted for water
• Amniotes


  • Egg equipped with an amnion, permeable to water
  • Inside the egg may be liquid substances
  • albumin (white portion) provides embryo water, yolk for energy,
  • chorion allows exchange of oxygen and carbon dioxide with external environment
  • Shells are protective calcareous structures that allow gas exchange
• amniotes


  • Amnioin- Liquid environment that protects from mechanical shock
  • Amniotic fluid - shock absorber.
  • yolk- contain the food of embryo
• Allantois


  • Fluid portion of the egg that accumulates waste products (urea)
• Reptilia (Sauropsida)


  • Ectothermic amniotes, air breathing
  • First amniotes before birds
  • Cornified epidermal cells (scales, plates, claws)
  • All regularly shed the outer layer of the skin
  • Cold blooded, metabolism and activity depends on environment
• Reptilian groups


  • Anapsida (no temporal fenestration)

  Synapsida (1 temporal fenestration)

  Diapsida (2 temporal fenestrations)
• Anapsida


  • Chelonians (turtles)
• Synapsida


  • Pelycosaurs (to birds)
• Crocodile


  Long snout, teeth visible
• Alligator


  Short snout, teeth hidden
• Archosaurs


  • Can regulate body temperature, have specialized breathing tubes & lungs
  • Ilium & pubis attached to vertebral column
• Carnosaurs


  • Carnivorous
• Aves


  • Well adapted for flight (feathers, endothermic)
  • Beak/bill, endothermic, oviparous, toothless
  • Light weight skeleton
• Aves evolution


  • Archaeopteryx - Jurassic, large skull, teeth, claws, long tail, feathered

  Hesperornithiformes - Cretaceous, flightless, teeth

  Ichthyornithiformes - Cretaceous, smaller, can fly
• Avian behavior


  • Nest building

  Courtship

  Parental care

  Migration - triggered by dropping temperature, dwindling food supplies, position of sun, topographical landmarks, magnetic clues, air pressure changes, low frequency sounds
• Avian classification


  • Archaeornithes - extinct, primitive wings, skull with teeth in both jaws

  Ichthyornithes - extinct, teeth in both jaws

  Hesperornithes - extinct, flightless, teeth

  Neornithes - modern birds
• Mammalia


  • Possess mammary glands (breasts)

  1. Prototheria (monotremes) - egg laying, 2 genera (platypus, echidnas)

  2. theria

  *Metatheria (marsupials) - young stay in mother's pouch, no placenta

  *Eutheria (placental mammals) - carry unborn young in uterus until birth
• 2 types of neornithes

  1. ratite- flightless bird, wings may be absent or rudimentary, sternum is broad and without keel
  2. carniate- flying, sternum is keeled, use feathers for steering during flight
• Amphibia phase 3

  • adaptation for weight
  • support walking
  • increased terrestrial activity
• Amphibia phase 4

  • loss of lateral line cannal and gills
  • reduction in size of limbs and girdles