Nov 29 - Animals Lecture #21 - Aves (Birds)1

All 3 have similar morphology character similarity o

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All 3 have similar morphology Character similarity o General therapod Elongate, S-shaped neck Highly versatile neck Tridactyl feet (i.e. 3 forward facing digits) Hollow, pneumatic bones (?) o +dromeosaurs: Were the nuts and bolts for the evolution of modern birds Wrist structure that permits “hand” turning Shoulder joints that allow arm flapping Key feature Feathers with symmetrical vanes Most likely used for thermoregulation Archaeopteryx and the origins of flight o Also had asymmetrical or flight feathers o Contour feathers covering body and differentiated “flight feathers” o Flight features with asymmetrical vanes But don’t believe they were good at flying Sternum not prominent Forelimb bones not fused Modern bones are fused to give additional strength Long tail Absent in modern birds Hindrance to flight Most likely had short flights Competing theories o Arboreal theory (top down theory) Based on tree climbers that jumped between trees Selected pressure over long period choosing animals that had increased distance and accuracy that can jump from tree to tree Selective pressures favoured increased distance and accuracy o Terrestrial theory (bottom up) Dromeosaurs terrestrial bi-pedal hunters Involved mechanism for short periodic flight Claws at end of wing tips Suggested to use for hunting although for arboreal used for climbing Skeletal elements for flight poorly developed Based on running around and using its wing to capture prey
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As you increase speed and jumping, you start to do short landing flights If you are more successful in doing these short landing flights, you are more successful on capturing prey Incipient wings evolved as traps
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  • Fall '08
  • thoracic vertebrae, feathers, Contour feathers, 2.0g, pygostyle

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