Sorry fat doesn't turn into muscle. If you started running and noticed your leg muscles are developing, it is simply becasue you are starting to loose fat and the muscles are strengthening.
haha fat morphing into muslce? Wouldn't that be great. To (not lieraly) turn fat into muslce, you just gotta do exercise and you will lose fat and gain muscle at the same time. To develop only muscle but keep fat there, weight train on your legs instead of doing aerobics