FIG. 1 is a perspective view of an all terrain vehicle showing my new design; FIG. 2 is a left side elevation view thereof; FIG. 3 is a right side elevation view thereof; FIG. 4 is a front elevation view thereof; FIG. 5 is a rear elevation view thereof; and, FIG. 6 is a top plan view thereof. All structures indicated in broken lines are not part of the design sought to be patented.