Morphological variation of the Pan talus relative to that of Gorilla

Abstract

Objectives Differences in talar articular morphology relative to locomotion have recently been found within Pan and Gorilla. Whole‐bone talar morphology within, and shared variation among, Pan and Gorilla (sub)species, however, has yet to be investigated. Here we separately analyze talar external shape within Pan (P. t. troglodytes, P. t. schweinfurthii, P. t. verus, P. paniscus) and Gorilla (G. g. gorilla, G. b. beringei, G. b. graueri) relative to degree of arboreality and body size. Pan and Gorilla are additionally analyzed together to determine if consistent shape differences exist within the genera. Materials and Methods Talar external shape was quantified using a weighted spherical harmonic analysis. Shape variation both within and among Pan and Gorilla was described using principal component analyses. Root mean square distances were calculated between taxon averages, and resampling statistics conducted to test for pairwise differences. Results P. t. verus (most arboreal Pan) talar shape significantly differs from other Pan taxa (p < 0.05 for pairwise comparisons) driven by more asymmetrical trochlear rims and a medially‐set talar head. P. t. troglodytes, P. t. schweinfurthii, and P. paniscus do not significantly differ (p > 0.05 for pairwise comparisons). All gorilla taxa exhibit significantly different talar morphologies (p < 0.007 for pairwise comparisons). The more terrestrial subspecies of G. beringei and P. troglodytes exhibit a superoinferiorly taller talar head/neck complex. Discussion P. t. verus exhibits talar morphologies that have been previously related to more frequent arboreality. The adaptations in the more terrestrial G. beringei and P. troglodytes subspecies may serve to facilitate load transmission.

Trabecular bone variation in the gorilla calcaneus

“…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, Junno, et al, 2018; 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, 2021b, 2023; Jabbour & Pearman, 2016; Knigge et al, 2015; Prang & Tocheri, 2024; Tocheri et al, 2011). These studies have found many differences among the taxa with respect to locomotor repertoires, such as relatively shorter feet in G. b. beringei for greater terrestriality and more asymmetric talar trochlear rims in G. g. gorilla , which has been suggested to reduce shearing stresses when the foot is loaded on uneven substrates as an adaptation for arboreality (Dunn et al, 2014; Harper et al, 2023; Inouye, 1992; Jabbour & Pearman, 2016; Knigge et al, 2015; Ruff et al, 2022; Ruff, Burgess, Junno, et al, 2018; Ruff, Burgess, Squyres, et al, 2018; Schultz, 1934; Tocheri et al, 2011). There are many morphological differences in calcaneal external morphology among the taxa including a flatter calcaneocuboid joint with a shallower cuboid facet pivot region and a mediolaterally wider calcaneal tuber in the more terrestrial G. b. beringei (Harper et al, 2021b; Jabbour & Pearman, 2016; Prang & Tocheri, 2024).…”

“…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).…”

“…These studies have found many differences among the taxa with respect to locomotor repertoires, such as relatively shorter feet in G. b. beringei for greater terrestriality and more asymmetric talar trochlear rims in G. g. gorilla, which has been suggested to reduce shearing stresses when the foot is loaded on uneven substrates as an adaptation for arboreality (Dunn et al, 2014;Harper et al, 2023;Inouye, 1992;Jabbour & Pearman, 2016;Knigge et al, 2015;Ruff et al, 2022;Ruff, Burgess, Squyres, et al, 2018;Schultz, 1934;Tocheri et al, 2011). There are many morphological differences in calcaneal external morphology among the taxa including a flatter calcaneocuboid joint with a shallower cuboid facet pivot region and a mediolaterally wider calcaneal tuber in the more terrestrial G. b. beringei (Harper et al, 2021b;Jabbour & Pearman, 2016;Prang & Tocheri, 2024).…”

A statistical analysis of human talar shape and bone density distribution

“…Weighted spherical harmonics (SPHARM) is one such method to effectively analyze the shape of small, irregularly shaped objects, such as the talus. [33][34][35] This method has been implemented by previous studies to examine variation in tarsal shape in both humans and primates. 34,36 Additionally, a statistical description of the distribution of bone density that investigates sex and age variation will be advantageous to implant design.…”

“…[33][34][35] This method has been implemented by previous studies to examine variation in tarsal shape in both humans and primates. 34,36 Additionally, a statistical description of the distribution of bone density that investigates sex and age variation will be advantageous to implant design. With such information, surgical devices such as total ankle replacements could be further customized for a patient's specific age and sex, potentially resulting in an increase in implant success.…”