Morphological correlates of distal fibular morphology with locomotion in great apes, humans, and Australopithecus afarensis

Abstract

Objectives Recent studies highlighted the importance of the fibula to further our understanding of locomotor adaptations in fossil hominins. In this study, we present a three‐dimensional geometric morphometric (3D‐GM) investigation of the distal fibula in extant hominids and Australopithecus afarensis with the aim of pointing out morphological correlations to arboreal behavior. Methods Three‐dimensional surface meshes of the distal fibula were obtained using computer tomography for 40 extant hominid specimens and laser scanner for five A. afarensis specimens. Distal fibula morphology was quantified positioning 11 fixed landmarks, 40 curve semilandmarks, and 20 surface landmarks on each specimen. A generalized Procrustes analysis (GPA) was carried out on all landmark coordinates followed by Procrustes ANOVA. Principal component analysis (PCA) was performed on the GPA‐aligned shape coordinates. Kruskal‐Wallis tests and Mann–Whitney test were performed on scores along PCs. Results Great apes are characterized by a shorter subcutaneous triangular surface (STS), more downward facing fibulotalar articular facets, more anteriorly facing lateral malleolus and wider/deeper malleolar fossa than humans. Within great apes, orangutans are characterized by more medially facing fibulotalar articular facets. Australopithecus afarensis shows a unique distal fibular morphology with several traits that are generally associated more to arboreality and less to bipedalism such as a short STS, a more anteriorly facing, laterally pointing malleolus and deeper and larger malleolar fossa. Conclusions The distal fibula morphology is indicative of locomotor patterns within extant hominids. The 3D‐GM method presented here can be successfully used to further our understanding of arboreal adaptations in fossil hominins.

Sexual Dimorphism in the Fibular Extremities of Italians and South Africans of Identified Modern Human Skeletal Collections: A Geometric Morphometric Approach

“…The aim of this study was to highlight patterns of sexually dimorphic form variations in the fibular proximal and distal epiphyses in individuals of three different populations from Italy and South Africa belonging to identified modern skeletal collections (19th–20th century), utilizing a 3D GM approach [ 54 ]. Our study provides a new method for sex estimation on the fibula, potentially applicable in bioarcheology [ 20 ], where this method may find primary implementation, and forensics, offering moderate to high accuracy (80–93% for Italian populations) for identification in case of the recovery of isolated fragments of this bone.…”

“…While the specific relationship between a muscle and its tendon can change depending on several factors (e.g., muscle/tendon specificity, loading degree, age), in our sample, such variations are minimal, since all individuals possess similar activity levels (i.e., sedentary lifestyle [ 76 ], and age variations in the samples are similar ( Table 1 ). Therefore, tendon size could be used to assess muscle size [ 54 ]. Finally, we did not find significant shape/form sex-related variation regarding articular orientation in agreement with previous studies on sex variations of the bones of the leg [ 28 ], but see also [ 77 ].…”

Comparability of skeletal fibulae surfaces generated by different source scanning (dual‐energy CT scan vs. high resolution laser scanning) and 3D geometric morphometric validation

“…A template of 142 landmarks and semilandmarks (Table 1 and Figure 1 ), modified from a previous version published by Marchi et al ( 2022 ), was applied to targets (both CT‐ and laser scanner‐generated models) utilizing Viewbox 4 software (dHal Software). Curve and surface semilandmarks were allowed to slide along the curves/surfaces to minimize the thin‐plate spline (TPS) bending energy between the target and the template obtaining geometrically homologous semilandmarks (Slice, 2005 ; Gunz & Mitteroecker, 2013 ).…”

“…Specifically, we test the accuracy and comparability of CT‐ and laser scanner‐generated meshes in a sample of 13 modern human fibulae, considering the whole bone surface but also focusing on the extremities. The fibula has so far not been included in previous mesh accuracy assessments, despite its digitization in several biomechanical studies, alongside the tibia (e.g., Marchi, 2005 , 2007 , 2015b ; Marchi, 2015a ; Marchi et al, 2019 , 2022 ). In addition, fibular 3D meshes are routinely utilized in reconstructive surgery, in the assessment of tibio‐fibular syndesmotic reductions performed after ankle fractures (e.g., Ebinger et al, 2013 ; Souleiman et al, 2021 ) and surgical planning of mandibular reconstructions from fibular free flaps (e.g., Damecourt et al, 2020 ; Ni et al, 2021 ; Ren et al, 2018 ).…”

Linking the proximal tibiofibular joint to hominid locomotion: A morphometric study of extant species

“…Our results show that all great apes separate from one another (Figure 6) due to distinctive proximal fibular morphology. Previous studies found significant differences in relative (to the tibia) fibular strength (Marchi, 2007(Marchi, , 2015a and distal fibular morphology (Marchi et al, 2022) among taxa that engage more frequently in vertical climbing behavior (Pan and Pongo) compared to those that are more terrestrial (Homo and Gorilla). The authors linked these differences to larger peroneal muscles in the former, a feature that has generally been associated with arboreal great apes (Aiello & Dean, 1990;McLean & Marzke, 1994;.…”