Feather

Feather is a unique skin growth that forms the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty.

Structure and function

Feathers are among the most complex integumentary appendages found in vertebrates and are formed in tiny follicles in the epidermis, or outer skin layer, that produce keratin proteins. The β-keratins in feathers, beaks and claws — and the claws, scales and shells of reptiles — are composed of protein strands hydrogen-bonded into β-pleated sheets, which are then further twisted and crosslinked by disulfide bridges into structures even tougher than the α-keratins of mammalian hair, horns and hoof.

Evolution

Feathers are not simply limited to birds, but were also present on a variety of coelurosaurian dinosaurs. The discovery of feathers in the small theropod dinosaur Sinosauropteryx has revolutionized the way we think of dinosaurs.

Types of feathers

There are two basic types of feather: vaned feathers which cover the exterior of the body, and down feathers which are underneath the vaned feathers. The pennaceous feathers are vaned feathers. Also called contour feathers, pennaceous feathers arise from tracts and cover the entire body.

Feathers and flight

While many types of feathers are more generalized in structure, the flight feathers of adult birds and bird wings are specialized in a number of ways to aid in flight. The feathers on the leading edge of the wing (the primaries) are narrower than those at the trailing edge (the secondaries and tertiaries), and this difference is often accentuated by the presence of notches or serrations on the forward margin of the primaries of some birds.

See also

• Bird
• Dinosaur
• Sinosauropteryx
• Flight feathers

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