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Feathers are the most complicated integumentary structure among the vertebrates. Like hair, nails and scales, feathers are integumentary appendages ; skin organs that form by controlled proliferation of cells in the epidermis, or outer skin layer, that produce keratin proteins. They insulate birds from water and cold temperatures and provide colour which is sometimes used as camouflage against predators and sometimes as a means of visual communication. Although individual feathers are very light, a bird's plumage weighs two or three times more than its skeleton.
Feathers evolved from the scales of reptiles, but their original function remains mysterious. Although birds use feathers primarily for flight, several dinosaurs have been discovered with feathers on their limbs that would not have functioned for flight. One theory is that feathers originally developed on dinosaurs as a means of insulation; those small dinosaurs that then grew longer feathers may have found them helpful in gliding, which would have begun the evolutionary process that resulted in the proto-birds Archaeopteryx and MicroraptorMicroraptor was a small, bird-like dinosaur related to the dromaeosaurs. It lived during the early Cretaceous. Like Archaeopteryx it demonstrates the close evolutionary relationship between birds and dinosaurs, as it had long feathers on its limbs and tai.
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, providing an insulating layer. The vaned feathers include the remigesA bird's flight feathers which are attached to the rear portion of the wing bones. Remiges are given different names depending on their position on the wing: primaries which are connected to the hand bones. Usually eleven in number although there are exce (flight-feathers), the rectricesA type of vaned feather found in a bird's tail. There are usually twelve rectrices in all, six in each half of the tail. See also remiges. (tail-feathers) and the contour feathers which are distributed over the whole body. A typical feather features a main shaft, called the rachis. Fused to the rachis are a series of branches, or barbs; the barbs themselves are also branched and form the barbules. These barbules have minute hooks for cross-attachment. At the base of the feather, the rachis expands to form the hollow tubular calamus, or quill, which inserts into a follicleIn botany, a follicle is a type of simple dry fruit produced by certain flowering plants. It is regarded as one the most primitive types of fruits, and derives from a simple pistil or carpel (see flower). At maturity, the follicle dehisces (splits open) a in the skinThis article is about skin in the biological sense. For other uses of skin see skin (computing) and skinhead. Regarding exposure of the skin to be seen by others, or prevention of this, see nudity, nudism, modesty, clothing. Fruits such as oranges also ha.
A bird's feathers are replaced periodically during its life through molting, new feathers are formed through the same follicle from which the old ones were fledged.