Well, it’s been found that a mutation in chicken embryos can cause them to grow teeth, but they never survive long enough to hatch (Article
here). It’s likely that birds still possess the genes for teeth, but they are inactive. I don’t know if it is possible for those genes to be “switched on” in such a way that a bird develops teeth and survives to adulthood.
Anyway, I’ve always interpreted your wingtail characters as being sort of intermediate between dinosaurs and true birds. After all, they have dinosaur characteristics such as hands and a long, bony tail, a little like
Archaeopteryx or
Microraptor. (Didn’t you even say that their design was originally inspired by Guido?) And the fact that their wings have membranes clearly sets them apart from other birds. The way I see it, they’re sort of like “alternative birds”; a type of feathered dinosaur that developed a different way to fly (membranous wings with feathers on them instead of purely feathered wings). Thus they’re very similar to birdsóand could be even called birds, just as
Archaeopteryx is called a bird despite the high likelihood that it was not a direct ancestor of birdsóbut they’re technically not true birds.
And, of course, creatures in animated films that are toothless in reality are often given temporary teeth for the same reasons you described. So arguably, wingtails could still be toothless.
Okay, new question: Is that notch in Sky’s tail vane a scar of some kind? If so, where did he get it?