Moistness is an in-game mechanic related to Oxygen and having to do with water. Moistness is an indicator of how long a dinosaur can survive on land before they begin to take damage.
Terrestrial Dinosaurs/Aerial Dinosaurs Edit
Terrestrial/Aerial dinosaurs have no moistness since they live on land. They instead use oxygen.
Aquatic dinosaurs have a moistness meter of 30, meaning once that reaches 0 they take damage while still on land or above the surface of the water. Some aquatic dinosaurs have oxygen as well, such as Mosasaurus.
Hybrid dinosaurs have no moistness, but they do have increased oxygen and the ability to swim with no major speed loss.