The Cross River Gorilla is only found in an area of about 12,000km2 around the headwaters of the Cross River, spanning the border between Nigeria and Cameroon. This is the most northerly and westerly position in which gorillas are found, and lies about 300km from the nearest population of Western Lowland Gorilla, and 200km from the recently discovered gorillas of the Ebo Forest, in Cameroon (13).
Gorillas eat fruit, tree bark, pith, terrestrial herbs and leaves. Although they seem to prefer fruit, this is scarce during the dry season so they must depend on other sources of nutrition. The season of fruit scarcity is longer in this more northerly region (4-5 months) (19).
Long term studies are ongoing at both the Afi and Kagwene sites, which have already discovered differences in the diet, ranging behaviour, and grouping patterns of Cross River Gorillas in comparison with Western Lowland Gorillas. There may also be significant differences between groups of Cross River Gorillas. (13)
Cross River Gorilla skulls are smaller than those of other gorillas. Male Cross River Gorilla skulls are particularly distinct. Cross River Gorillas have the smallest mean cheek tooth (molar and premolar) surface area, and the difference in this measure is greater between them and the Western Lowland Gorillas than between the two types of eastern gorilla. There is no corresponding difference in body size, so Cross River Gorilla skulls are smaller relative to their body size, as well as absolutely. (9)