Around 30 mya (million years ago) the Alps and the Himalayas rose up and became the world's first major (tons of square miles) mountain ranges. If you were a boring old Wildebeest or even a Zebra, you wouldn't have much reason to venture up onto the rocky wastes of this new, more vertical, land. And if the victims of the great hunger hunt won't go up, neither will the predators. Of course, eventually, it is going to look like a good place to someone, and they are going to give it a try. Who is going to do well in this upright new world? Why not the little guys who already are used to scampering up and down trees? I wonder if we didn't go through a major bird-eating phase at this time, since birds would have had a good time up there, too. We were already used to thinking of the world in terms of up and down, along with right and left.