Thanks for all of the suggestions!
So I ended up picking up the Bestiary: Predators and it is a pretty comprehensive catalog of modern day animals, with a small mix of prehistoric animals. The CRs range from 1/8 to 9, which is fine for an E6 sandbox game. Most of the bigger and deadlier creatures are aquatic, which... well, is natural.
Overall I'm impressed with this pdf. It takes a historical and academic approach to the subject, which is great if you want to go for a simulationist route to your game.
The Animal Archives seems to be zeroing in on a lot of real and imaginary apex predators, many of which are prehistoric predators, which a typical party of adventurers would perhaps gulp a bit when it charges them. I haven't picked up these three pdfs though. It's broken up into three pdfs. I guess it would have been more compelling if it was just one pdf for around $10. I want to see what I can get out of the Bestiary pdf first before trying out the Animal Archives.