Friday, May 7, 2010

The Anatomy of a Feather - A Marvel of Design

The common feather is a miracle of design. And note that it is based on the repetition of a basic design element.
The structure of the shaft is a tiny tube. The barbs are the same design (but smaller) at an angle to the shaft. The barbules are again the same design (but smaller) at an angle to the barb. Similarly with the hooklets.
Thus the complete feather is developed from the repetition of a basic tube.
"Extending from both sides of the quill is a linear cluster of barbs containing a majority of the feather's pigment. Together, the barbs and the quill constitute the body or vane of the feather. Branching at a 40-degree angle on each barb is a network of barbules with interlocking hooklets that provide both stiffness and flexibility to the feather. These hooklets allow a split vane to be resealed making it whole again."

This is the design of the feather of a modern bird and it appears to also be the design of the fibers in the pterosaur wing.

Additional info:
"Whatever their function, feathers evolved by selection for a follicle that would grow an emergent tubular appendage. Feathers are inherently tubular structures. Feathers are composed of a suite of evolutionary novelties that evolved by the duplication, hierarchical organization, interaction, dissociation, and differentiation of morphological modules. The unique capacity for modular subdivision of the tubular feather follicle and germ has fostered the evolution of numerous innovations that characterize feathers."
"While feathers have been suggested as having evolved from reptilian scales, there are numerous objections, and more recent explanations have arisen from the paradigm of evolutionary developmental biology.[2] Theories of the scale-based origins of feathers suggest that the planar scale structure was modified for their development into feathers by splitting to form the webbing; however, the developmental process involves a tubular structure arising from a follicle and the tube splitting longitudinally to form the webbing.[1][2]"

"The question of why a relatively complex machinery was necessary to produce a relatively simple object is not directly answerable (Feduccia, 1985, 1995Go). Perhaps the most primitive structure unit was cable-like and reflected the filamented keratin macromolecule. At each level, the follicle and the feather is an amalgamation of smaller, simpler units. Emergent properties, such as the curve in the rachis, while functionally significant, are the result of simple processes such as differential growth. From the elemental barb, all other morphology follows, as the barb is the simple structural unit."

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