Arboreal signals in the skeletal proportions of the Gorilla foot

Postcranial skeletal proportions in living apes have been linked to patterns of arboreal behaviors within and between populations, offering a comparative baseline for interpreting arboreal behavior in fossil hominoids. We quantified metatarsal and proximal phalangeal lengths across all five pedal rays in Gorilla, comparing western lowland gorillas (Gorilla gorilla gorilla), low- and high-elevation Grauer's gorillas (Gorilla beringei graueri), and two ecologically distinct mountain gorilla (Gorilla beringei beringei) populations: those of Bwindi Impenetrable National Park, Uganda, and the Virunga Massif (Volcanoes National Park, Rwanda). The Bwindi sample, assembled from individuals recovered by the Mountain Gorilla Skeletal Project between 2017 and 2025, represents the first substantial pedal dataset for this population. After separately scaling element lengths by estimated body mass and hindlimb length, Bwindi gorillas' third and fourth metatarsal lengths fell consistently between those of the more arboreal western lowland and highly terrestrial Virunga gorillas, while proximal phalangeal and hallux lengths varied little across populations. Additionally, Virunga gorillas showed longer second metatarsals compared to other populations, a feature we link to their strongly terrestrial locomotor habits. In comparing relative manual and pedal element lengths from the same individuals, metacarpals were relatively longer than metatarsals across all populations in rays 2-5, with this pattern reversed in the hallux; among these, only the second ray showed a significant interpopulation difference, with western lowland gorillas exhibiting relatively longer metacarpals than all other groups. Though interpopulation differences in the lengths of pedal elements were generally weaker than those found in the manual elements of the same individuals, these findings suggest that habitat-associated variation in foot morphology can be detected between populations of gorilla subspecies, underscoring the value of fine-grained, population-level skeletal comparisons for refining locomotor inference in the hominoid and hominin fossil record.