Fish scale the surface, interacting only with the riblet tips, not causing any high-veloctiy flow in the valleys. Since this high velocity flow now only interacts with the riblet-tip, which is a very small surface area, the momentum transfer which causes drag is now much lower than before, thereby effectively reducing drag. Also, this reduces the cross-stream velocity fluctuations, which aids in momentum transfer too. The rough, sandpaper-like texture of shark and ray skin, coupled with its toughness, has led it to be valued as a source of rawhide leather, called shagreen. One of the many historical applications of shark shagreen was
Leather-Winged Bat Leather-Winged Bat "Leather-Winged Bat" is a well-known English folk song about a collection of "birds". The song's most used cast members are usually bat, a wood pecker, a blue bird, owl and turtle dove (bats, of course, technically being mammals and not birds). However, depending on the artist, the song can have different creatures. Such as Peter, Paul and Mary's 1969 version which has a bat, a black bird, wood pecker, turtle dove, and a blue jay. Each "bird" has something to say about love and courtship in some sort of rhyming manner. It was recorded by Burl Ives on