When was the eocene geological period?

Eocene period - began about 55 million years ago, and lasted between 15 million and 17 million years. During this period animals, fishes and plants made enormous evolutionary progress, in some cases coming very close to those familiar today. During the eocene period the climate got warmer, and many plants became extinct. But new plants, especially flowering varieties, evolved, giving the world's vegetation a more modern appearance. On land many familiar mammals appeared to replace more primitive animals. Horses were abundant, there were also tapirs and rhinoceroses. Pigs and camels began to appear but increased only slowly, because of constant attacks from the now extinct sabre toothed tigers.