I really like the first one, Tucker. Shame you can see the fence in the background, but that can't always be avoided. Love the way the elephant and the log are almost the same color, and the way its ears are flapping!
I wouldn't hesitate to post photos of this sort in the Nature & Wildlife forum, as long as you are clearly not trying to pass them off as anything other than what they are. Naming the thread with "Zoo" in the title makes it pretty clear that you aren't trying to suggest you were on an African safari.
Considering the thread seems to be titled "Knoxville Zoo"..a thread you obviously clicked on...one has to wonder the point of such a tremendously rhetorical comment. Considering that there doesn't appear to be a separate section here on thephotoforum dedicated to zoo or nature center photography (or even pet photography for that matter), to me, wildlife seems just as appropriate as any. Or was your comment simply intended to denigrate the OP's work simply because it wasn't captured in the "wild"? If so, as a frequent zoo shooter myself I would certainly take a great deal of offense to such a comment.
Personally one of my greatest joys is "critter photography", whether it's in the wild or in some zoo-like facility (or even pics of my own domestics here at home). That said however, while I can't speak for others, living here in Ohio I simply don't have the opportunity to capture many such creatures as lions, elephants, meercat, giraffe, orangutan, etc.. As jcdeboever said about Detroit, you simply don't see such creatures running down the streets of greater Cleveland. That however does NOT in any way suggest that images of "captive" animals deserve any less credit. As far as I'm concerned, unless the images were intended to misrepresent some photojournalistic representation of something other than what was clearly indicated, the images should be judged on their merits as images, not specifically where they were captured. In other words, if it's otherwise a good image, why should it matter whether the creatures in question were captive or not? I shot a great many images at a local nature center that I used to volunteer for...should those images deserve less credit because those creatures were also captive???
Again I'm quite curious as to the point of such an utterly rhetorical comment.....
To the OP: I like the composition of the elephant, however with both the elephant and the lion, I would urge you to check your color balance...both of those shots look REALLY yellow on my screen. Also, while I do like the pose of the gorilla, the image could be a bit sharper (especially around the eyes) and I'm not sure the image really warrants the need for black and white.
As for the lion, I'm not sure I really care for the pose there...as is, the lion appears to be looking out of frame. While I will admit that, as with people photography, I do prefer it when "critters" look at the camera (animals or people, it's all about "the eyes"), in an instance such as this, I might have composed the shot differently by placing the lion's head in the right third of the frame/composition and allowing a little "space" for the lion to be looking through. Since that's obviously a square crop there, I would actually be interested to see the original...I suspect there might have been a better way to crop it.