I really like the idea of this deck, but man, there just aren't a lot of apes out there, so it's hard to come with any suggestions for creatures. Which sucks, since the creature count is kinda low imo. If you aren't that dedicated to the idea of every creature counting as an ape AND representing an ape in the artwork, I would definitely go the changelig/
shapeshifter way too (which you've already done a little bit) - try out
Masked Vandal, it's really great! Otherwise, I like the pun route that @Bonethousand suggested, where you go with cards like
Apex Devastator; ie cards that either references apes or ape-related stuff.