Mandrills belong to the Cercopithecidae family, the Old World Monkeys. Some characteristics of the Old World Monkeys include: a narrow nose and palate, flattened nails on the digits, cheek pouches, and ischial callosities, pads of thickened skin on the rear end that provide a weight bearing surface as the monkeys sit (Rowe 119).
In addition to the brilliant colors on their faces, males have coloration on their hind ends - light purple that fades into a reddish purple color. The pronounced differences in size and coloration between males and females are referred to as sexual dimorphism.
Male mandrills have large, menacing canine teeth that may be up to 2.5 inches long. The teeth are used in threatening facial expressions and as weapons. Mandrills also have skin glands, including a sternal gland in the middle of the chest. "Males older than 7 years scent-mark, but alpha males scent-mark more frequently" (Rowe 142).
"Cheek pouches open beside the lower teeth and extend down the side of the neck; they can hold the equivalent of a stomach load of food, leaving hands and feet free for running and climbing", an important feature for a primarily terrestrial animal (Lincoln Park Zoo).