To make convincing-looking CGI animals, it takes more than a detailed and textured volumetric or polygon-based model. For movement, it's essential to model the inner, as well as the external anatomy
Here's a Behind the Scenes of SSE's advert (by the agency Adam and Even/DBB) which shows how to convincingly make a CGI ape look real. They've done a good job as you can see in the video below.
The advert was crafted by The Mill, who explain here how they did it.