You can "freeze" your Dino at the Deep Gorges.
While frozen, you can not use this dino, but it no longer counts in your total Dinoz limit of 18 or if you have the Wood Unique skill Leader, 21. You can only unfreeze your frozen Dino if you are under your limit of unfrozen/active Dinoz.
You can still gain the overall benefits of even if the Dinoz who bear them are frozen. For example, a lot of players put Unique skills in dinoz and a couple of others to stay alive long enough to get to the Deep Gorges to freeze them. Some players also freeze dinoz because they didn't turn out very well, like getting elements they didn't want them to get. It is also a good idea to go for leader in the first of your 5 dinoz because it gets really boring when you have an egg (Kabuki, Ferross, or Mahamuti) and you are waiting for your 18th dinoz to get that precious skill.