Feather

A feather is a branching integumentary structure made of keratin, characteristic of birds and some other dinosaurs. Its branching parts form a lightweight surface used for insulation, display, and flight.

Calamus: The hollow, basal part of a feather shaft that anchors the feather in the skin. It is the feather’s attachment point and connects the vane-bearing shaft to the bird.
Feather development: The process by which a feather forms from a skin follicle through coordinated growth and differentiation. It describes how a feather’s branching architecture emerges from the follicle.
Flight feather: A stiff feather of the wing or tail that contributes to aerodynamic forces in flight. Its asymmetrical vane and strong shaft help generate lift, thrust, or steering.
Feather evolution: The evolutionary history of feathers and their diversification among theropod dinosaurs and birds. Feather form changed over time, with flight arising after feathers already existed.
Hair: A keratin-rich filament growing from the skin of mammals. Hair is another keratinous covering, but it lacks a feather’s branched vane.
Rachis: The central shaft of a feather, extending from the calamus and supporting the vane. Its stiffness supports the branching parts that give a feather its shape.
Molt: The periodic shedding and replacement of feathers in birds and other animals. Molt renews worn feathers and can replace them in organized patterns.
Filoplume: A slender, hairlike feather with a small tuft of barbs near its tip. Filoplumes are associated with sensing the position and movement of other feathers.
Sinosauropteryx: An Early Cretaceous theropod dinosaur known from fossils preserving filamentous integument. Its fossil covering documents simple featherlike structures outside modern birds.
Scale: A plate- or flap-like skin covering found in animals including reptiles and birds. Scales cover skin without the feather’s branching shaft-and-vane architecture.

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