They can use this tail as an extra arm to grip or even hang from branches—no Old World monkeys have such a tail. A gripping tail is particularly helpful to howler monkeys because they rarely ...

They have been lost in humans as we evolved more stable speech. Latin American species of howler monkey, capuchin squirrel monkey and Peruvian spider monkey have the largest membranes of all primates.

My adventure of a lifetime began in 2015 when I was asked to follow the tree-top lives of Costa Rica’s gravity-defying howler monkeys (Alouatta palliata palliata). Image by Justine Allan.

MEXICO CITY--It’s so hot in Mexico that howler monkeys are falling dead from the trees. At least 83 of the midsize primates, who are known for their roaring vocal calls, were found dead in the ...