Ecological divergence and calcaneal‐cuboid morphology in gorillas

Abstract

ObjectivesGorillas are diverse behaviorally and ecologically with higher frequencies of arboreality and frugivory observed in populations living at lower altitudes compared to those living at higher altitudes. Previous studies have shown that the more arboreal western lowland gorilla has hallucial tarsometatarsal and talocrural joint morphologies associated with enhanced hallucial abduction and foot inversion capabilities whereas the more terrestrial eastern gorilla does not. Here we examine how known ecological and behavioral differences among gorillas relate to variation in calcaneal and cuboid morphology. Specifically, we test whether gorillas that climb more frequently (i.e., western lowland and lowland grauer gorillas) have cuboid‐metatarsal and calcaneocuboid morphologies that facilitate increased foot mobility compared to those that climb less often (i.e., mountain and highland grauer gorillas).MethodsWe quantify the relative areas of articular and nonarticular surfaces, angles between articular surfaces, articular surface curvatures, the relative length and depth of the calcaneocuboid joint, and the relative size of the calcaneal tuber using three‐dimensional models of gorilla calcanei and cuboids (n = 90 and 81, respectively).ResultsOur results, based on univariate and multivariate analyses, show that western and eastern gorillas follow our predicted arboreal‐terrestrial morphocline in terms of their calcaneal and cuboid morphology; however, highland and lowland grauer gorilla populations do not.ConclusionsThis study has implications for understanding gorilla foot function and the evolutionary processes responsible for producing the morphological patterns among living gorilla populations. Future studies of gorilla morphological diversity may provide a useful comparative model for studies of locomotor evolution in extinct clades.

Trabecular bone variation in the gorilla calcaneus

“…Calcaneal external morphology is quite variable among extant hominoids and is functionally correlated with known locomotor variation (Harper et al, 2021a, 2021b, 2022; Kidd, 1999; Latimer & Lovejoy, 1989; McNutt & DeSilva, 2020; Nozaki et al, 2021; Prang, 2015, 2016; Prang & Tocheri, 2024). For example, more arboreal non‐human hominoids have a cuboid facet that is relatively larger and has a deeper pivot region, two features that have been suggested to increase mobility at the calcaneocuboid joint during inversion and eversion (Gebo, 1992; Harper et al, 2021a, 2021b; Prang & Tocheri, 2024).…”

“…The hominid calcaneus (Figure 1), in particular, could be a valuable skeletal element to study given its multiple articulations with other bones, its role as a lever for the plantarflexor muscles, and its weight-bearing role during the stance phase of the gait cycle. Moreover, it has already been demonstrated that its external shape is correlated with different locomotor behaviors (e.g., Gebo, 1992;Harper et al, 2021aHarper et al, , 2021bHarper et al, , 2022Kidd, 1999;Latimer & Lovejoy, 1989;Levine et al, 2014;McNutt & DeSilva, 2020;Nozaki et al, 2021;Prang, 2015Prang, , 2016Prang & Tocheri, 2024;Schmitt & Larson, 1995;Zeininger et al, 2020).…”

“…to increase mobility at the calcaneocuboid joint during inversion and eversion (Gebo, 1992;Harper et al, 2021aHarper et al, , 2021bPrang & Tocheri, 2024). More terrestrial hominoids (humans and nonhumans) have relatively wider and more robust calcaneal tubers that may be adaptations to higher hindlimb loads associated with terrestrial locomotion (e.g., Harper et al, 2021aHarper et al, , 2021bLatimer & Lovejoy, 1989;Prang, 2015;Schmitt & Hanna, 2004).…”

“…Postcranial variation among gorilla taxa has been extensively studied over recent years (e.g., Fatica et al, 2019;Jabbour & Pearman, 2016;Ruff et al, 2022;Ruff, Burgess, Squyres, et al, 2018), with many studies focusing on external morphological variation in the foot and ankle (e.g., Dunn et al, 2014;Harper et al, 2021bHarper et al, , 2023Jabbour & Pearman, 2016;Knigge et al, 2015;Prang & Tocheri, 2024;Tocheri et al, 2011).…”

Mary Marzke, PhD: A pioneer and innovator in the study of the evolution of the human hand

“…Several of these papers combine Mary's lifelong pursuits of methods to quantify complex shape variation to improve understanding of the relationship between primate functional morphology and locomotor behavior, spanning the foot, leg, hand, vertebrae, and pelvis. Friesen et al (2024) examine variation in talar and medial cuneiform shape among chimpanzees and bonobos using 3D geometric morphometrics, while Prang and Tocheri (2024) explore variation in gorilla calcaneal‐cuboid morphology in relation to differences in ecology using biomechanically‐informed 3D measurements of the size and orientations of their articular surfaces and the calcaneal tuber. Two articles focus on covariation of morphology within the wrist and hand, also applying 3D geometric morphometrics: (1) Bardo et al (2024) examine the first carpometacarpal joint and (2) Vanhoof et al (2024) investigate distal ulnar and triquetrum shape.…”