When I pick up RPG rules the thing that stands out to me is lists: lists of character classes, skills, magic items, spells, monsters and so on. So when looking for precursors it's worth checking out lists as well as fiction and games.

I picked this book up on eBay. Published in 1967. I find it hard to believe that D&D wasn't influenced by this even though Gygax explicitly denies having read it. (It was republished under a different name and I bet he knew that version.)

Every single animal in the Animal section is in the Monster Manual 1e. Even the difference in speed between the two camels is explicitly mentioned. And why did the Monster Manual have entries for both Mammoths and Mastodons?

Anyway, this is a fun genre of book.