The northern muriqui (Brachyteles hypoxanthus) is one of two species of muriqui. They are also known as woolly spider monkey because they exhibit the woollen pelt of woolly monkeys and the long prehensile tail of spider monkeys. Muriquis are the largest extant New World monkeys. They can reach long and weight up to . The northern muriqui is a critically endangered species that is unusual among primates in that they display egaltarian tendencies in their social relationships. This species is endemic to the Atlantic Forest region of Brazilian states of Rio de Janeiro, Espírito Santo, Minas Gerais and Bahia. Their diets, travel patterns and reproductive cycles are seasonally determined. The size of each group can fluctuate as females will move between groups of monkeys. Morphology and identification Northern muriquis exhibit features that allow them to utilize all of their limbs and tail for travel and obtaining food items. As they spend much of their life in the canopy of forests, they use brachiation as a form of locomotion utilizing all four limbs and their tail. Evolutionary features that further aid these large atelids are elongated hook-like fingers, and shoulder that allows for a wide range of movement. As these monkeys are primarily suited for life in trees, they still venture down to the ground to drink from water sources, consume soil or to obtain ripe fruit that has fallen. Northern muriquis can be individually recognized by their natural markings and facial features, such as fur color and patterning, ear shape, and face shape and pigmentation. In contrast to the southern muriqui, northern muriqui exhibit a lack of sexual dimorphism, southern muriqui exhibit dimorphism in their canines, but northern muriqui have kept vestigial thumbs. Ecology Diet Northern muriqui are frugivorous and folivorous, but they also rely on flowers, bark, twigs, stems and soil to supplement additional nutritional needs. The amount of what each group eats depends on seasonality, wherein they will consume foods higher in calories, which results in higher fruit consumption during the wet season, and increased leaf consumption in the dry season. This affect how groups of B. hypoxanthus travel as they forage for food, as bigger family groups need to travel further to attain adequate food sources. The muriqui also utilize vertical niches when foraging, as they can access all levels of forest, from the floor to the canopy. Muriqui group home ranges overlap, so unrelated groups of