Lecture 8: Origin of Birds and Flight

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Lecture 8 Origin of Birds and Flight
Reading Chapter 33 591-592, Chapter 48
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• Two main controversies- from whom and how did
  flight originate?
• Origin of birds
• Origin of flight
• Flight in vertebrates passive to self powered
• Structure and function of wings
• Two major hypotheses for origin of powered
  flight
• Bird systems-breathing, osmoregulation, and
  development

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Ancestry of Birds

• Birds are feathered dinosaurs, ancestry from
  theropod dinosaurs (Saurischians)
• Birds share many features with reptiles eg.
  shelled aminiote egg but ancestral retentions
• Birds share other features not in all reptiles
  but in some i.e. Archosaurs e.g. 4 chambered
  heart, endothermy
• Birds uniquely developed flight

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Earliest Bird- 150 myaArchaeopteryx
lithographica
would have been classified as a reptile except
for feather impressions
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Archaeopteryx lithographica
flight feathers
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Modern birds -Diversity
9,600 species of living birds
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Passive Flight Parachuting/Gliding
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Powered active flight
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Bird Skeleton
 Fused clavicle (furcula) Sternum (breast
bone) with keel (attachment flight muscles)
Wing lift support Tail steering landing
control
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Bird Skeleton
air spaces
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Origin of Flight Two hypotheses
Ground Up (Running) Quadruped-Facultative
biped --obligatory biped--forelimbs increased use
prey capture thrust-selection for more lift
Trees down (Arboreal) Tree
dwelling--leaping between trees--
parachuting--gliding--active powered flight
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Origin of Flight Two Theories
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Bird Respiration
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Osmoregulation
nasal salt glands in marine birds excrete
excess salt  countercurrent exchange
system blood flows counter to salt
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How does a limb form?
Homeobox genes