My money is on it being a black domesticated house cat. I'd say it's in the 10-15 pound range. Animals often look bigger than they really are. A good way to really gauge how big it was is to stand where you took the pictures and then take something of known size and place it where the cat was seen while taking the pictures. Take a picture of that item and compare. Often times you will go wow, that thing was much smaller than I thought. I do that a lot with bobcats I get on game camera that I think are big. I put a 8.5" by 11" piece of paper on a stake in front of the game camera in the same spot where the cat was and have it take a photo. When you look at the two photos, one of the unknown cat and then of the paper, you can get a pretty good idea just how big the cat is. I often find that bobcat I thought was 40 pounds turns out to be a more commonly sized 20 pounder...
If it is a black jaguar, you should play the lottery as they are rare in the Amazon where the more common color is fairly common. The black color phase is almost unheard of in the subspecies that is found along the Texas/Mexico border.
If it's a black mountain lion/puma/catamount etc, then it is a first. There has never been a documented melanistic mountain lion ever.
