Monkeys are not the only animals from which the fauna evolved.  Life existed even before the appearance of monkeys on earth, and with the evolution of time, various species of animals have evolved through metamorphosis.  The biggest difference between monkeys and primitive animals was their tails.  Because monkeys had tails than other animals and primitive animals did not have any tails. The primitive animals were larger than monkeys in terms of size and their brains were bigger and bigger in shape.