Multiple pens are easy to make, wood is cheap. Although I started with mine sorted, you can sort yours by making a single gap between pens, then nudging the correct animals through it, re-fencing after they're through. Don't use wheat, just push them. :) If that's too annoying, then make small separate pens (with a single opening) all around your main pen, then wait until some animal of the correct species moves in randomly - close the gap, build a channel to your new pen.
Or, possibly the easiest way - just bring a group of any mix of animals into the new pens , with wheat. Once you have two of any species in the new pen, you can slaughter the unwanted species, as well as the remaining ones in the previous pen :)