BIO2231 Lecture Notes - Lecture 20: Bird Anatomy, Air Sacs, Reptile Scale
Lecture 20 – Vertebrates III: Birds & Mammals
• Feathers did not evolve for flight because some birds are flightless
Archaeopteryx
• Earliest known bird – extinct theropod dinosaur
• Beak, claws, feathers
Bird Characteristics of Modern flying birds – Class Aves
• Animal with feathers
o Homologous to reptile scale – highly modified
▪ Modified for display and sensory purposes
o Hooked barbs to form flat plane
o Keratinised
o Growth from base
o Branching structures that dry out
o Annual moult
• Leg scales
o Forelimbs modified as wings
o Modified sternum with keel for attachment of flight muscles
• Toothless beak
• Fused vertebrate
• Fused clavicula
• Fully ossified skeleton
o With air cavities
o Due to strength and weight
• Birds – highest metabolic rate and
metabolism
o Double circulation, 4 chambered
heart
• Highly efficient lungs – flow through parabronchi airsacs
• Flow through lungs
o Ventilation from airsacs
▪ Air sac fills up before air
goes into lungs
o Continuous flow of air over
lungs
▪ Lungs are linearly
arranged
o Air flows unidirectionally over
gas exchange surface
o Channels – parabronchi
o Inhalation
▪ Air sac’s fill
o Exhalation
▪ Air sacs empty, lungs fill
• Endothermic, very high metabolic rates
o Regulate own body temperature 40-41˚c
• Fast moving
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