Currently, we have 3 standard Enclosure Bonuses ("Bonus/es"):
Shared Dig Site: All species in an enclosure must be found in the same formation.
Shared Region: All species in an enclosure must be located in the same geographical region, outlined by the Paleopedia¹.
Shared Time Period: All species in an enclosure must share a geological time period.
However, you may note a very key caveat: All species in the enclosure must share the criterion, or that Bonus is forfeit. I have considered a few ways to retool this system to breathe fresh life and remove that caveat.
[1] Do away with Shared Dig Site: Doing so allows for more versatility in enclosures, and allows players to mix formations without having to consider the Bonus lost.