After some playing around and experimenting, here's some findings and tips.
-Animals that are Neutral to each other, or that have a Likes/Neutral relationship (using Ichthyosaurus and Liopleurodon as my examples for the latter) can cohabitate peacefully if you give them extra space. Liopleurodon requires six lagoon segments to reach its maximum comfortable area, while Ichthyosaurus only requires four segments. So, if you want to have them together, add 50% to 100% of the lesser requirement to the greater, so your lagoon would be comprised of eight to ten segments. This will give them room to have areas of no territorial overlap and also prevents the Ichthys from wearing themselves out panicking from the Lios. Also, you'll want a lot of fish feeders, something like 5 or so, because depending on how many individuals of each species you have (and territory size need slightly increases for each individual, the six segments are for the maximum five per clutch) they can have "Missing Fish" displayed even if they have their minimum feeder needs, since there's more individuals. Having a lot of fish feeders ensures that they're content with their food supply which means little to no aggression. I had five Lios and eight Ichthys in a nine-segment lagoon with five feeders for nearly an hour and there was no aggression or killing each other.
-For dinosaurs it's a similar deal, though a bit trickier since you build the enclosures from scratch. Using Allosaurus and Metriacanthasaurus as examples, build and adjust an Allosaurus enclosure so it has 100% contentment in its total area and everything else about 10% or so above the minimum requirement. Then expand the enclosure by, say, one full fence length along one or two sides, put in a second water spot in the new area away from the water already in, and put in a second goat feeder in the expanded area and a meat feeder somewhere in the middle of the enclosure or so. That should give the Metrias plenty of space to have their own non-overlapping territory areas since they're smaller than Allo, and plenty of food for everyone. As a secondary tip, try to have the minimum number of individuals for the larger animal possible, it might help curb their aggressiveness.
-For the herbivores, it's simply a matter of knowing who likes who and who's indifferent to who. You can have up to four different species together if you mix and match carefully, one example being an enclosure with Pachycephalosaurus, Chasmosaurus, and Crichtonsaurus, with two dinosaur species who like each other and the third but the third only likes one and is indifferent to the other. Also keep an eye on what each species eats, because even if they're compatible you might tear your hair out trying to balance their food needs if they all eat something different. This goes doubly for the sauropods not named Nigersaurus and Amargasaurus, as they generally need huge areas devoted to their food that few other dinosaurs share.
Hope that all helps you out!
