Synopsis

The Oligocene had arrived, ushering in a profound shift in climate that eradicated a fifth of all species. The expansive tropical forests and plains that defined the Eocene had receded, now clinging only to the equatorial regions. In Mongolia, a seasonal desert reigned, its landscape populated by creatures of immense size, reminiscent of the dinosaurs' age. Here prowled Hyenadons, predators the size of modern rhinoceroses; Entelodonts, brutish pigs of comparable bulk; and, most impressive of all