The Amazon and its major tributaries such as the Xingu, Tapajós, Madeira, Purus and Rio Negro form barriers to the geodispersal of plants, animals and even insects. Thus the white-fronted capuchin (Cebus albifrons) and hairy saki (Pithecia hirsuta) are found west of the Tapajós, while the white-nosed saki (Chiropotes albinasus) is only found east of the river.
