Feathers

FEATHERS

•Feathers originate in a skin layer deep under the outer layer that forms scales.

•Feathers probably arose as new structures under and between reptile scales, not as modified scales. Many birds have scales on their lower legs and feet where feathers are not developed

• feathers did not evolve for flight. They evolved for some other function and were later modified for flight.

•Feathers may have evolved to aid thermoregulation.

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 the overlying 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 the developing feather

A collecting site for metabolic wastes that are then carried away in the blood stream

- The feather follicle develops around its base as the feather 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 barbs stretch out of their cramped quarters and the shaft elongates.

•The contour feathers used for flight are known as remiges and rectrices, can be divided into three groups: primaries, secondaries and tertiaries.

•The primary feathers propel the bird through the air.

•The secondary flight feathers run along the "arm" of the wing and sustain the bird in the air, giving it lift.

•The Tertiaries are the few flight feathers and the numbers 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 ; the base of the shaft is the calamus ; the vane- bearing segment is the rachis ; each vane consists of a row of barbs that 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 as Filoplumes

-Are hair-like feathers consisting chiefly of a threadlike shaft

-They are scattered throughout the skin among contour feathers

- The long colorful feathers of a peacock are filoplumes