First they get the bison on the run, then filter out the weak and vulnerable and select the perfect target. Striking together, wolves can bring down prey many times their own size. A million such chases must have taken place across these plains and we can still find echoes of these distant life-or-death encounters.

 

Not all evidence lies locked in bone and rock. These pronghorn antelopes among the great survivors of the ice age reveal a lot about the distant past. As well as being tough enough to stand extremes of temperature, they're famous for their speed. 

 

A sprinting pronghorn can top 60 miles an hour and cruise at 30 for several hours. This kind of speed requires a very finely tuned physique. Pronghorn have a massive heart and run with their mouths gaping open, forcing extra air into their huge lungs.

 

But what's the point? No predator can run this fast. Even the wolves can only manage 40 miles an hour. So why do pronghorn feel this need for speed? This is why—once there was a predator here that could outrun the pronghorn a cheetah.