Ground Whales are big friendly animals who bury themselves in the ground for protection from the Piranhakeets.
It resembles a small right whale with greasy gray skin, a fish-like tail fin, and four stubby legs. Its mouth is quite large and rock-like and can easily be mistaken for a cave when it is buried underground, as it apparently leaves it open while underground to either breath or catch small prey. They also have a blowhole on their back like a regular whale.
They appear to be docile and harmless and do not appear to eat large creatures like cavemen. They are also cowardly as they hide underground to avoid the ferocious Piranhakeets. They can also be tamed and used as riding animals.
In the Movie
The Croods mistake one's mouth for a cave, and enter it. Once they enter, the mouth closes. Thunk then says "Hey, look! This cave has a tongue! Awesome!" and they are shot out through the spout. A Ground Whale was later eaten by hungry pack of about 10,000 Piranhakeets. All that was left of it were it's bones.
At the end, Thunk appears to have tamed one and is seen riding it in a race with his family and their pets (showing that Ground Whales are fast runners).
- In a McDonalds commercial, the Croods are seen riding one to a McDonalds restaurant.