Once upon a time I'd have dug up the threads to check if my theories have been discussed, but I'm starting to realize this is unfeasible. So if you know that this has been discussed feel free to direct me there.
Anyway, skyeels. We know most Roshar animals have some form of carapace, especially land animals (the fish in purelake, as far as I know, are regular fish). The exceptions are almost universally actually from Ashyn - like horses, or chicken, or cows and sheep. Some horses specifically have adapted to Roshar - Rishadiums. So my question is, are skyeels similar? Did they, too, come from Ashyn as just eels or something and then evolved to fit Roshar better? Or are they just one of numerous Roshar creatures that are ever so slightly different? Roshar does seem to have fish similar to ours, after all, so maybe skyeels naturally evolved from an existing species?