It's a bit of a tricky balance. The classic Traveller book and supplement actually did a good job for generic critters based on their niche - really more broadly their behavior. But it didn't even attempt to give guidelines on types of critters - major phylums (phylae ?). For ecosystems, devising some basics like: the most visible lifeforms are homeothermic hexpodal feathered creatures with hammer-shaped heads and four eyes. So there should be decisions based on things like that, on dominant senses, on maximum complexity and on how energetic the ecosystem is (temperature and biomass could play a part).
To make it more interesting, in the Third Imperium, you also need to worry about invasive species from the Ancients and from 10,000 years of Vilani civilisation.
First half of such a book could be procedures, guidelines, and tables, with the second half example creatures. Like Highguard for critters. Actually sort of like the Robot book now that I think about it...