What are your thoughts on stories using anthropomorphic fantasy? Is this a sub-genre all by itself and is it popular enough to be marketable?
Anything that is good enough can be marketable. That said, it is not to me knowledge an official sub-genre, so you shouldn't say that's your genre in your query.
What is an official sub-genre? It gets a bit hard to tell. Genres are actually pretty much determined these days by in what section the bookstores places them, and a lot of things get lumped together. Why some things are in sci-fi/fantasy and some things are in fiction & literature (i.e. general fiction) are a mystery to me, but that's why I'm not a Barnes and Noble buyer. As for sub-genres, they're only really relevant in certain cases particular to the genre, and generally they're not worth thinking about in the query because we can probably figure out the sub-genre from the summary. If it's about elves in New York, it's urban fantasy. If it's about a small-town amateur detective who solves crimes, it's a cozy. If it's a fictionalized account of the last days of General Custer, it's historical fiction. You don't really need to tell us that; we know the business, plus we think it's hilarious (in a bad way for you) when you get your sub-genre wrong, or list multiple genres in the hopes that you will convince us that it will be a crossover hit. (Man, I've done that. I was such a dork)
A good way to tell if your genre is "popular" is to go to a large bookstore and see how many titles on the shelves would fall in the same category as your work. I'm guessing in this case it would be very few, and I'm even counting the Dragons of Pern stuff.