Head and body length is 610-764 mm and tail length is 52-76
mm. Weights of males are average 25 kg and 11.5 kg. for females.
This species is the largest of all monkeys measuring 508 mm
at the shoulder and weighing as much as 54 kg. The facial features
are distinguished be an outgrowth of six ridged and grooved
bone which are seen as prominent ridges along the length of
the nasal bones. In adult males the skin in the grooves is purple
and blue on the ridges. The area between each set of ridges
is a bright scarlet extending forward to the muzzle and around
the nostrils. Females have less pronounced ridges, lacking the
purple coloration in the grooves and the scarlet is replaced
by black. The buttock pads of both males and females are furless
and have a lilac tinge with reddish purple edges. This coloration
may facilitate group movement through thick vegetation. The
brightly colored skin of M. sphinx becomes intensified
when the animal becomes excited. The fur on the top of the head
is a tawny green and the underparts are yellowish.
Preferred habitat is dense rainforest where the heavier males
travel along the ground and the smaller females and babies are
found mid-level in the trees. After foraging on the ground for
fruits, plant material, mushrooms, invertebrates, and sometimes
small vertebrates, they enter sleeping trees in the late afternoon.
ranges are relatively large, spanning 40-50 sq km. Social groups
are comprised of 1 adult males, 5-10 adult females and an average
of 10 juveniles. These smaller groups some together in the dry
season, resulting in troops of as many as 200 individuals. Adult
males without harems are solitary. Reproduction appears to be
seasonal with most births occurring between the months of January
and April in the population studied in Gabon. Gestation is 168-176
M. sphinx is found south of the Sanaga River in Cameroon;
Rio Muni (Equatorial Guinea); Gabon; and Republic of Congo.