The Amazon rainforest, along with the Atlantic and Corrado Forests, is considered to have and maintain the greatest biodiversity in the world.

An excerpt from the article 31 facts about Brazil

Scientists estimate that the total number of plant and animal species in Brazil may approach four million, mostly invertebrates. Brazil has the largest number of both terrestrial vertebrates and invertebrates of any country in the world. It has many thousands of species, many (if not most) of which are still undiscovered.

The larger mammals found there are carnivores: pumas, jaguars, ocelots, the rare bush dogs and foxes, and herbivores: peccaries, tapirs, anteaters, sloths, opossums, and armadillos.

Northern rainforests abound with many species of New World monkeys.