Geographic variation in gorilla limb bones

Area of Science:

• Primatology
• Paleontology
• Zoology
• Bioarchaeology

Background:

• Gorilla systematics has been a focus for primatologists, conservationists, and paleontologists, leading to proposals for two distinct species: Gorilla gorilla (western gorilla) and Gorilla beringei (eastern gorilla).
• Previous research on postcranial differences primarily compared mountain gorillas (G. beringei beringei) with western lowland gorillas (G. g. gorilla).
• Geographic variation within eastern and western gorilla species, particularly in limb bone morphology, remained underexplored, as did the taxonomic status of subspecies like Gorilla gorilla diehli and G. b. rex-pymaeorum.

Purpose of the Study:

• To investigate geographic diversity in gorilla limb bone skeletons.
• To evaluate proposed subspecies (e.g., Cross River gorilla, Tshiaberimu, and Kahuzi gorillas) within the context of geographic variation.
• To examine forelimb and hindlimb skeletal differences between eastern and western gorilla species and their subspecies.

Main Methods:

• Collected 43 linear measurements from limb bones (humerus, radius, metacarpal, hand phalanx, femur, tibia, calcaneus, metatarsal, foot phalanx) of 266 adult gorillas.
• Represented populations included G. b. beringei, Gorilla beringei graueri, G. g. gorilla, and G. g. diehli.
• Employed comparisons of means and principal components analyses to assess skeletal variation and population clustering.

Main Results:

• Eastern and western gorillas were clearly differentiated by skeletal measurements, with eastern gorillas exhibiting smaller hands and feet, both absolutely and relatively.
• Gorilla subspecies and populations clustered consistently by species, though G. g. diehli showed similarities to eastern gorillas in hand and foot size.
• Subspecies within G. beringei were less distinctly separated than the two main species, and G. b. graueri populations displayed variability, with Kahuzi and Tshiaberimu specimens not clustering together.

Conclusions:

• Geographic variation significantly influences gorilla limb bone morphology, supporting the distinction between eastern and western gorilla species.
• The findings suggest that higher-altitude Pleistocene refugia may have played a role in shaping observed patterns of geographic variation in gorillas.
• The study provides skeletal evidence relevant to ongoing discussions about gorilla taxonomy and subspecies recognition, particularly for G. g. diehli.