origin of feathers: their initial purpose ethan weitz matt kennedy jennifer greenwood
TRANSCRIPT
Origin of Feathers:Their Initial Purpose
Ethan WeitzMatt KennedyJennifer Greenwood
Development of Feathers
Stage 1: The follicle originated with a cylindrical epidermal invagination around the base of the feather papilla.
Stage 2: The inner layer of the collar differentiated into horizontal barbs which grew unbranching keratin filaments.
Stage 3: The rachis is formed by the fusion of barb ridges on the midline of the follicle.
Stage 4: Proximal and distal barbules created the first closed, pennaceous vane.
Stage 5: Additional structural diversity allowed for asymmetrical flight feathers with vanes of different widths.
Hypotheses of Feather Evolution Flight
After stage I, feathers become flat allowing for flight
Interlocking barbules Stages II & IV
Thermoregulation Stage I feathers are thin, numerous, and
pliable Stage II feathers are heavier and filamentous Heat Shielding
Protection from solar radiation Water Repellency
Possible by Stage II Communication and Crypsis
Sexual selection Camouflage
Defense Pointed keratinaceous structures Stage I
For what purpose did feathers evolve first?
Hypothesis 1: Flight
Escape predators Migration Leaping, jumping and other
fighting behaviors associated with sexual selection could have been pre-adaptive to flight.
Jumping to avoid predation may have lead to leaping between trees, then parachuting, gliding, and eventually active flight.
Video
Hypothesis 2: Thermoregulation & Heat Shielding
Using reptiles as a conceptual model it is suggested feathers arose as adaptations to intense solar radiation.
Lizards in hot climates have elongated scales.
Having broad, insulating structures allowed the animal to control the gain and loss of heat.
Hypothesis 3: Water Repellency
Pennaceous structure and the keratinous material of feathers allows water to roll off the surface.
Some birds posses an oil producing gland which they spread over their feathers to increase water repellency.
Hypothesis 4: Communication and Crypsis
Sexual selection through plumage displays
Sexual dimorphism Camouflage
Hypothesis 5: Defense
Modern feathers-not so much.
Early in feather development the pointed, keratinous structures were similar to the modern porcupine.
Which hypothesis do you support?
FlightThermoregulation and heat shieldingWater repellencyCommunication and CrypsisDefense
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