Trampling and Bioturbation
Depending on shapes, bones generally have preferred stable orientation; in most cases these are horizontal, with specific sides up or down. Trampling and bioturbation can disturb this pattern into near vertical positions, also plant growth and soil movement can alter these positions.
Wildebeests fighting their way to safety, crush
and trample anything in their path, even each other.
Any former remains would be scattered and destroyed
in the process.