The gorilla walks upright like a human being.
At about 00:12:45 into the film, two lesbian cave-women are having sex. The one on the top removes the fur loincloth of the one on the bottom - but we can clearly see the loincloth is attached with a *modern* gold nylon cord tied in a knot.
The cave-women all wear lipstick and eye shadow and their hair looks like they just came from a beauty parlor.