...is "ptero-" = wing?

Remember BC (the comic strip)'s apteryx : "I am a wingless bird with hairy feathers." a-pter = without wings.

Come to think of it, arachno-dactyly is a condition of very long slender limbs, like a spider's (usually associated with the descritpion of Marfan's Syndrome, and attached to the description of Abraham Lincoln as a hypothesis). If dactyls are fingers or arms or even legs, why is the poetic dactyl a "foot" ?

"Because dactyls aren't fingers, Silly," I hear you say, "they've been feet all the time!" Yes? No?