Definition of "pycnofibre"

While the metal frames, styrofoam bulk and resin wings comprised the majority of the models, the details that would bring them to life – eyes, scars, pycnofibres, scales and colour – needed to be added before the models could really look vital.

2012, A. J. Veldmeijer, Mark Witton, Ilja Nieuwland, Pterosaurs: Flying Contemporaries of the Dinosaurs, Sidestone Press, page 119

Many [pterosaurs] had furry coats made up of hair-like filaments known as pycnofibres, which covered their bodies and parts of their wings.

2014, Albert J. DeBenedictis, Evolution or Creation?: A Comparison of the Arguments, 3rd edition, Xlibris, page 254