TERTIARY PERIOD

Following the demise of the dinosaurs at the end of the cretaceous period, the tertiary period (65-1.6 million years ago), which formed the first part of the Cenozoic era (65 million years ago present), was characterized by a huge expansion of mammal life, Placental mammals nourish  and maintain the young in the mother's uterus; only three orders of placental mammals existed during cretaceous times, compared with 25 orders during the tertiary period. One of these 25 included the first hominid, Australopithecus, which appeared in Africa. By the beginning of the tertiary period, the continents had almost reached their present  position. The  Tethys sea, which had separated the northern continents from Africa and India, began to close up, forming the Mediterranean sea and allowing migration  of terrestrial animals between  Africa and Western Europe. India's collision with Asia led to the formation of the Himalayas. During the middle part of the tertiary period, the forest dwelling and browsing mammals were replaced by mammals such as the horse, better suited to grazing the open savannahs that began to dominate. Repeated cool periods throughout the tertiary period established the Antarctic as an icy island continent.