West of Eden - Harry Harrison

The first volume in an epic trilogy which introduces an alternative world where dinosaurs still reign supreme.
Sixty-five million years ago, a disastrous cataclysm eliminated three quarters of all life on Earth. Overnight, the age of dinosaurs ended. The age of mammals had begun.
But what if history had happened differently? What if the reptiles had survived to evolve intelligent life?
In WEST OF EDEN, bestselling author Harry Harrison has created a rich, dramatic saga of a world where the descendants of the dinosaurs struggled with a clan of humans in a battle for survival.
Here is the story of Kerrick, a young hunter who grows to manhood among the dinosaurs, escaping at last to rejoin his own kind. His knowledge of their strange customs makes him the humans' leader...and the dinosaur's greatest enemy.