Mantled Howler Monkey

A Mantled Howler Monkey spotted high up in trees near Lake Arenal, Costa Rica.

This one was impressively demonstrating its prehensile tail using it as an extra limb to climb through the canopy.

I think it may be the Golden-Mantled Howler (Alouatta palliata palliata) subspecies but I'm not sure.

The mantled howler is one of the largest Central American monkeys, and males can weigh up to 9.8 kg (22 lb). It is the only Central American monkey that eats large quantities of leaves; it has several adaptations to this folivorous diet. Since leaves are difficult to digest and provide less energy than most foods, the mantled howler spends the majority of each day resting and sleeping. The male mantled howler has an enlarged hyoid bone, a hollow bone near the vocal cords, which amplifies the calls made by the male, and is the reason for the name "howler". Howling allows the monkeys to locate each other without expending energy on moving or risking physical confrontation.