Lesson 4

• What are some downsides to being an amphibian?

  Moisture loss, predation, and vulnerability to environmental changes, shell-less eggs
• Amniotic Egg

  Self-Contained

  Stable

  Protective

  Made of Extraembryonic Membranes

  • Chorion & amnion are outgrowths of the body wall
  • Chorion - surrounds entire contents of the egg
  • Amnion - surrounds just the embryo
  • Allantois - outgrowth of hindgut behind yolk
  • Stores nitrogenous wastes
  • Provides gas diffusion
  • Left behind when embryo emerges

  Alnumin

  • Prevents drying
  • Cushion

  
• Fenestrations: Holes in the skull with space for muscles to expand and lengthen.
• What are some benefits of fenestrations?

  Stronger jaw muscles

  Larger gape
• How many fenestrations does an anapsid skull?

  0
• How many fenestrations does a synapsid skull have?

  1
• How many fenestrations does a diapsid skull?

  2
• Separation of the Mammal & Reptile/Bird Lineages

  Few derived terrestrial characteristics at separation

  • Independent development = convergent evolution

  Adaptations

  • Water conservation in excretion & respiration
  • Locomotion & high rates of ventilation
  • Endothermy & insulation
  • K-selection
  • Fast moving predators and prey
  • Flight
• How does sustained locomotion differ between reptiles and mammals

  Reptiles

  • Air moves lung to lung, not in and out of the body
  • Axial bending
  • Prevents air from moving in and out
  • Limited supply of energy = anaerobic metabolism

  Mammals

  • Air is forced into and out of the lungs
  • Dorso-ventral bending
  • Limbs underneath trunk
  • Shorter tail
  • Loss of ribs in loin area
  • Allows for bipedalism
  • Development of diaphragm
  • Separates pulmonary & abdominal cavities
  • Movement does not interfere with locomotion
  • Locomotion enhances function of diaphram
  • Fore-aft movement of legs

  
• What is notable about Sauropsids?

  Bipedalism - loss of ribs

  • Birds, many dinosaurs

  Gastralia & cuirassal breathing

  • Rib lever mechanism to laterally expand or contract abdominal cavity

  Rib movement & increased trunk flexibility

  • But also respiration diminishes greatly when moving

  Faveolar lung

  • Numerous branching patterns
  • Size and distribution of gas-exchange units varies
  • Cuplike chambers line the walls of airways
  • Ediculi, faveoli, or air capillaries
  • Posterior region of lung may store air or act as a bellows

  
• What is notable about synapsid lungs?

  Limited locomotion = no need for high rates of fas exchange

  Alveolar lung

  • Tree like dichotomous branching
  • Alveoli - terminal cuplike chambers filled with capillaries

  
• Why are synapsid and sauropsid lungs so different

  Synapsids - Paleozoic O2 was high

  • Larger internal surface area
  • Relatively long diffusion distances between blood and air in alveoli
  • Larger pressure gradients

  Sauropsids - Mesozoic O2 was low

  • Pumping of heart pushes air thru lungs when not actively breathing - unidirectional flow
  • Partitioning into air sacs and gas exchange regions
  • Thin barriers/short diffusion distances
  • Low pressure gradients
  • Internal divisions in lungs increase gas exchange capacity
• What are some concerns with high blood pressure?

  Rapid blood movement

  Forces plasma out of capillaries and into the air spaces

  Differing blood pressures depending on direction of flow = septum in ventricle

  Solved via 3 chambered heart

  • Evolved independently several times in sauropsids

  
• What is a result of the locomotion, heart, and lung adaptations seen in sauropods?

  Sustained locomotion & reorganization of musculature + heart & lung adaptations = consumption of energy (like ATP) = increased metabolic activities

  Some insulation still needed

  • Paradox = insulation provides no advantage without a higher metabolic rate but heat produced via higher metabolic rate is lost without insulation