A pennaceous
feather has a stalk or quill. Its basal part, called a
calamus, is embedded in the skin. The calamus is hollow and has pith formed from the dry remains of the feather pulp, and the calamus opens below by an
inferior umbilicus and above by a
superior umbilicus. Pennaceous feathers on the wing, and elsewhere, where stresses related to flight or other activities are high, are accordingly attached especially strongly. This strong attachment is accomplished by ligaments under the skin, which in some birds and other
feathered dinosaurs results in raised bumps or marks along the rear forelimb bone (
ulna). These bumps, called quill knobs (ulnar papillae), are often used as an indirect indication of strongly-attached forelimb feathers in
fossil species, and can also indirectly indicate the number of secondary
flight feathers in a given specimen.
Flight feathers (
remiges and
rectrices) are specialized types of pennaceous feathers,
adapted for high
loadings and often strongly asymmetric for improved
flight performance. ==See also==