National Geographic : 1987 Mar
(below left). Most endangered of the Brazilian marmosets, it has only recently been studied in the wild. Brown howler monkeys (left) are sometimes chased by the larger muriquis when the two compete for fruit. Their roars echoing through the forest, brown howlers number more than 600 at Montes Claros. The three-toed sloth, a vegetarian related to arma dillos and anteaters, is still fairly common. Only moments old, this sloth's tiny infant (farleft) was born in photographer Andy Young's vehicle after the Yale Univer sity doctoral candidate res cued the mother from a forest patch being cleared by fire.