Sometimes I find cool pictures when I'm looking for something else. These are all public domain, which means you can use them any way you wish.
This actual primate looks too Sword & Planet to be real. I like the colors.
From something titled Adventures in Skitzland. Saw it on the OBI scrapbook blog.
Guar, musk ox, American bison. These bring back good memories of reading encyclopedias in my grandma's junk-filled garage. I'll leave it to someone more skilled than me to remove the old paper color without messing up the rest.