If it's the Followers section on p27:

"Followers: Crypt Defenders receive only one follower at the appropriate level. This follower becomes the next defender of the site whenever the Crypt Defender retires or moves on. If the site is not a permanent one, the follower leaves with the Crypt Ranger as an apprentice."

I interpret this as getting that Animal that you're looking for, but as others have said, chat with your DM about identifying, finding, and then training an animal that'd be appropriate to whatever environment that you're in. Like, you won't find a Ferret in the depths of the ocean, etc, ya know?

My question, would that Ferret (or other targeted animal) have advanced HD to account for your level?