Topic summary
Quill knob
Extracted from the Wikipedia article Pennaceous feather.
Description
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.