Well, after several hours of searching for the few duplicate animals to sell and consolidating creatures in the few 3-creature habitats I had and migrating them to the free 4-creature habitats from events, I was finally able to clear enough land to get the two remaining 4 space-themed habitats to form the quad-habitat.
I must say that I'm disappointed in the final design as it seems that they did a slipshod job, particularly on the edges of the habitats. See for yourselves...
More than that, I'd have expected that each habitat would have had a different secondary element combined with Space. Instead, the Planetary Plateau was pure Space, the Stellar Garden was Nature, but both the Cosmic Field and Star Hill were Water, even though the design of the Star Hill was for clearly for Fire. And there's a fifth habitat that's pure Space, the Celestial Slopes. What happened to one combined with Lightning for the Lunar Drake?
The final combination does not look like what they showed in the popups. Not happy At least when you walk into a sleazy cafe the small prints at the bottom of their menus would say "The photos are for illustration only."