Based on this post, I did a 100% on two more planets with various fauna and checked all the ones that I've cleared before, and refined this a bit further. The list appears to always adhere to this order of creatures, with the caveat that if that type of creature is not on planet, its place is naturally taken by the next group of critters:
- Normal, land based carnivores or scavengers
- Normal, land based grazers etc
- Birds and other winged flyers
- Cave-dwellers (may appear on surface, but only near caves)
- Flying fish types ?
- Water based life-forms
The only really weird part on this set are the flying eel-looking critters, which inhabit the space between subterranean and aquatic creatures for some reason. I expected them to be with the birds, but that was not the case. Also of note is that creatures that just float on about 0.5- 1.0m above the surface are still considered land-based on this listing.
If anyone has noticed something that goes against this, please drop a word. There definitely is a pattern to establish, even if this is somehow inaccurate.