American Pronghorn: Social Adaptations and the Ghosts of Predators Past
The pronghorn antelope (Antilocapra americana) evolved, it would seem, to feed a host  of predators, ranging from coyotes and wolves to the long-disappeared saber-toothed tiger and American  cheetah. (Cheetahs, John A. Byers writes, were probably "the principal agents of selection that  prompted the evolution of astounding running speed in pronghorn"--a speed that has been clocked at  100 kilometers an hour.) Lacking many of those predators, today the pronghorn population has grown  throughout the American West, making the animals a common sight for ecotourists and residents alike.  Among other things considered in this thorough survey of pronghorn biology, Byers looks at "ghost  behavior"--patterns of action determined by ecological conditions that long ago changed. Horses, for  instance, remain herd-based social animals as a protective mechanism against predators, although, as he  writes, "predator-driven selection has been relaxed."