"Then, over the first two Epochs of the Tertiary (the Paleocene and Eocene), mammals exploded in number and variety. During this period (65 to 38 million years ago), primates, bats, the first ruminants and ancestral elephants appeared. Primates diverged into prosimians (future lemurs, lorises, galagos) and ancestral anthropods (future monkeys, apes, hominids) and, in North America, ancestral horses, rhinos and camels evolved. Canids (wolves, fox, dogs) and felines split from a common ancestor and the earliest cetaceans (whales, dolphins) returned to the sea."-
http://naturesblog.blogspot.com/2008/07/mammal-explosion.html