•Feathers probably arose as new structuresunder and between reptile scales, not asmodified scales. Many birds have scales ontheir lower legs and feet where feathers arenot developed•Feathers originate in a skin layer deepunder the outer layer that forms scales.
• feathers did not evolve for flight. Theyevolved for some other function and werelater modified for flight.•Feathers may have evolved to aidthermoregulation.
DEVELOPMENT OF A FEATHER - It is initiated by formation of a dermal papilla An early dermal papilla associated with formation of a placoid scales
-The growth of papilla, and its inductor effect on theoverlying epidermis, results in a pimple like elevation---- feather primordium, on the surface of the skin.-When the dermal papilla becomes vascularized :it is the source of nutrients and oxygen for thedeveloping featherA collecting site for metabolic wastes that are thencarried away in the blood stream
- The feather follicle develops around its base as thefeather primordium elongates - Between the dermal papilla and the epidermis, at the base of the feather follicle ---- a mitotically active growth zone proliferates tall columns of epidermal cells that pushes towards the distal tip of the growing feather, now a feather sheath- These epidermal columns separate from one another,cornify, and develop into barbs
-When the feather sheath splits open, the fluffy barbsstretch out of their cramped quarters and the shaftelongates.
•The contour feathers used for flight are known asremiges and rectrices, can be divided into threegroups: primaries, secondaries and tertiaries.
•The primary feathers propel the bird through theair.•The secondary flight feathers run along the "arm"of the wing and sustain the bird in the air, giving itlift.•The Tertiaries are the few flight feathers and thenumbers vary among species.
Morphological varieties of feathers:1. Flight Feathers •these feathers have developed into long showy plumes used in visual courtship displays
2. Covert Feathers - gives the bird its general shape
-Consists of a horny shaft and two flattened vanes ; thebase of the shaft is the calamus ; the vane- bearingsegment is the rachis ; each vane consists of a row of barbsthat have barbules and flanges -Arising from a notch, the superior umbilicus, is an afterfeather usually shorter than the main feather
3. Down Feathers -small, fluffy feathers lying underneath and between contour feathers. - They have a short calamus, with a crown of barbs arising from the free end, and no hooklets - It helps insulate birds
4. Hair Feathers-Also known asFiloplumes-Are hair-like feathersconsisting chiefly of athreadlike shaft-They are scatteredthroughout the skinamong contour feathers - The long colorful feathers of a peacock are filoplumes