Free jazz musical style did Miles Davis not play a major role in developing.

Miles Davis was a highly influential musician who played a major role in developing several styles of jazz music, including bebop, cool jazz, hard bop, modal jazz, and jazz fusion. However, one musical style that he did not play a major role in developing is Dixieland jazz. This style of jazz emerged in the early 20th century and is characterized by a lively and upbeat tempo, collective improvisation, and a strong emphasis on the melody.