The dinosaurs (non-bird) lived between 245 to 66 million years ago in the Earth, in a time known as Mesozoic Era, in that time some small mammals were alive. However, if you consider the humans species (Homo sapiens) the animals closer to dinosaurs that lived in the same period are the birds. Many scientists that study dinosaurs think that birds are direct descendents of one line of carnivorous dinosaurs. The dinosaurs and mammals coexist for 150 million years, the earlist known mammals were from 210 million years ago, and all the mammals today decend from the one line of these animals that survived.