Morphological differences in the calcaneus among extant great apes investigated by three-dimensional geometric morphometrics

Abstract

Investigating the morphological differences of the calcaneus in humans and great apes is crucial for reconstructing locomotor repertories of fossil hominins. However, morphological variations in the calcaneus of the great apes (chimpanzees, gorillas, and orangutans) have not been sufficiently studied. This study aims to clarify variations in calcaneal morphology among great apes based on three-dimensional geometric morphometrics. A total of 556 landmarks and semilandmarks were placed on the calcaneal surface to calculate the principal components of shape variations among specimens. Clear interspecific differences in calcaneal morphology were extracted, corresponding to the degree of arboreality of the three species. The most arboreal orangutans possessed comparatively more slender calcaneal tuberosity and deeper pivot region of the cuboid articular surface than chimpanzees and gorillas. However, the most terrestrial gorillas exhibited longer lever arm of the triceps surae muscle, larger peroneal trochlea, more concave plantar surface, more inverted calcaneal tuberosity, more everted cuboid articular surface, and more prominent plantar process than the orangutans and chimpanzees. These interspecific differences possibly reflect the functional adaptation of the calcaneus to locomotor behavior in great apes. Such information might be useful for inferring foot functions and reconstructing the locomotion of fossil hominoids and hominids.

Linear measurements and shape analysis in the calcaneus of selected dog breeds

“…Nozaki (2021) conducted a comprehensive 3D geometric morphometry study to explore morphological differences in the calcaneus among humans and great apes. The study revealed distinct differences in the calcaneal morphology between species.…”

Trabecular bone variation in the gorilla calcaneus

“…during toe-off, a flat posterior talar facet, and the presence of a large, plantarly positioned lateral plantar process (Boyle et al, 2018;DeSilva et al, 2019;Harper et al, 2021a;Latimer & Lovejoy, 1989;McNutt & DeSilva, 2020;Nozaki et al, 2021;Prang, 2016). These morphological trends relative to general locomotor behaviors have been observed both broadly among extant hominoid genera and at the species-level within the same genera, thus highlighting that the calcaneus is an informative location to investigate form-function relationships.…”

“…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).…”

“…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, 2021a, 2021b; Latimer & Lovejoy, 1989; Prang, 2015; Schmitt & Hanna, 2004). Humans exhibit a unique suite of morphological traits associated with bipedalism including a cuboid facet morphology that serves to transform the foot into a rigid lever during toe‐off, a flat posterior talar facet, and the presence of a large, plantarly positioned lateral plantar process (Boyle et al, 2018; DeSilva et al, 2019; Harper et al, 2021a; Latimer & Lovejoy, 1989; McNutt & DeSilva, 2020; Nozaki et al, 2021; Prang, 2016). These morphological trends relative to general locomotor behaviors have been observed both broadly among extant hominoid genera and at the species‐level within the same genera, thus highlighting that the calcaneus is an informative location to investigate form‐function relationships.…”

“…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).…”