The body covering of birds, formed as outgrowths of the epidermis and composed of the protein keratin. Feathers provide heat insulation, they give the body its streamlined shape, and those of the wings and tail are important in flight. Basically a feather consists of a quill, which is embedded in the skin attached to a feather follicle and is continuous with the shaft (rachis) of the feather, which carries the barbs. This basic structure is modified depending on the type of feather (see contour feathers; down feathers; filoplumes). Fossil evidence of feathers can be seen in some of the dinosaur ancestors of the birds, most famously in Archaeopteryx, which lived about 150 million years ago (see theropoda).