We can't. Our DNA matches up nicely with DNA from other Earth life forms, so we are native Earth beings.
Possibly, I suppose. Wasn't this an episode of Duckman?
If aliens exist, some alien races could possibly have six horns.
If aliens exist, some alien races could possibly have equine characteristics.
If aliens exist, some alien races could possibly have ursine characteristics.
If aliens exist, some alien races could possibly have caprine characteristics.
If aliens exist, some alien races could possibly have porcine characteristics.
If aliens exist, some alien races could possibly have musteline characteristics, such as weasels, skunks, badgers, otters, etc.
Possibly. I doubt were alone.
Possibly. This is a big problem in Arizona.
If aliens exist, some alien races could possibly have rodent characteristics, such as squirrels, etc.
If aliens exist, some alien races could possibly have leporine characteristics, such as rabbits and hares.
If aliens exist, some alien races could possibly have gastropod characteristics, such as snails and slugs.