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Major defining traits of birds
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Wing types
- eliptical, wing slots (cardinal)
- high speed wing, tapered (swallows)
- dynamic soaring wing, tapered (seagulls)
- high lift wing, wing slots (eagles)
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characteristics shared by reptiles and birds
- single occipital condyle on skull
- single middle ear bone
- lower jaw composed of 5-6 bones
- scales
- nitrogenous waste excreted as uric acid
- cleidoic eggs
- f=heterogametic, m=homogametic
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what was reptile like about archaeopteryx?
- tail
- boney jaw, teeth
- long legs for running
- reduced sternum
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what was bird like about archaeopteryx?
- feathers (wings and tail)
- reduced pelvis
- fused calvicle
- backward pointing toe (hallux)
- feathers for flying
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Thecodont hypothesis pros and cons
- evolved from thecodonts 230mya
- arboreal
- fossils of thecodont avian ancestors that resemble theropods b/c of convergent evolution
- Feduccia - digits of bird hand = dinosaur hand
- protofeathers
- microraptors not theropods
- flight should have evolved in arboreal species yet all theropods cursorial
- cons:
- no feathers on thecodonts
- less popular
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theropod hypothesis
- evolved from theropod dinosaurs 180mya
- curasorital
- trex dna sequencing similar to chicken and ostrich, not to croc
- presence of protofeathers on many theropods but not thecodonts
- cons:
- feet unlike modern birds, like thecodonts
- collagen fibers rather than protofeathers
- microraptors not theropods
- flight should have evolved in arboreal species
- impossible to reach running speeds
- reversed hallux not for running
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types of feathers
- contour feathers
- body feathers
- down feathers
- semiplume
- filoplume
- rictal bristles
- pterylae
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contour feathers
rachis/calmus w/ barbs
- barbs
- ramsu, barbules, barbicels
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flight feathers
- remiges - wings, asymetrical vane
- coverts - +survace area for lift
- retrices - tail, asymetrical, used for steering/breaking
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down feathers
- no rachis, barbicils
- barbs and barbules create fluffy tangle
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semiplume feathers
- rachis present
- barbicels absent
- under contour feathers
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filoplume feathers
- rachis
- no barbs (or only at tip)
- sensory function?
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rictal bristles
- calamus and rachis, no vane
- stiff
- used to trap food
- eyelashes
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pterylae
grows from base out in feather tracts
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what are feathers made of
90% beta-keratin
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evolution of feathers
- hypothesized stages
- unbranched, flexible, tubular elongation of placodes
- devel of barbs
- devel of rachis via fusion of barbs
- devel of barbules that branched from barbs
- why?
- escape from predation
- exploit new food sources
- disperse to new habitats
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