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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