The Cross River Gorillas: A Distinct Subspecies, Gorilla gorilla diehli Matschie 1904.

American Museum Novitates 3304: 1-55. 2000. doi: 10.1206/0003-0082(2000)3304<0001:TCRGAD>2.0.CO;2

This study presents the results of a new set of measurements made on museum specimens of gorilla skeletons from the Cross River headwaters. ... Considering their distinctiveness and geographic isolation, Cross River gorillas are best regarded as a distinct subspecies, G. g. diehli. Compared to other western gorilla populations, Cross River gorillas have smaller dentitions, smaller palates, smaller cranial vaults, and shorter skulls. Although Cross River gorillas do not seem to differ from other western gorillas in either body size or limb long bone lengths, measurements from a single male suggest that they may have shorter hands and feet and a larger opposability index than other western gorillas. Marked variation in the habitats of Cross River gorillas and insufficient data on behavior frustrate attempts to directly associate morphology with ecology. ....

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