Exploring the role of fibular extremities as indicators of mobility patterns and locomotor behavior in Homo sapiens from Mid- Late Upper Paleolithic to the modern age

The human fibular shape has been scarcely analyzed in anthropology. However, studies on athletes and human archaeological samples suggest the importance of including fibular structural properties to reconstruct mobility patterns in past populations. This study analyzes human fibular variation in relation to mobility patterns, environmental conditions, subsistence economies, and shoe use to further explore the role of this bone in reconstructing mobility patterns in past populations. The sample consists of 173 individuals from Italian archaeological and modern skeletal collections spanning the Mid-Late Upper Paleolithic to the twentieth century and includes hunter-gatherers, agriculturalists, herders, and post-industrialists. Virtual three-dimensional models of left fibulae were acquired by computer tomography and surface scanning. Fibular proximal and distal epiphyseal morphologies were investigated through 3D semilandmark-based geometric morphometric methods and compared among populations and mobility categories. Our analysis reveals a trend separating groups based on their subsistence strategy and chronology. Some fibular traits (e.g., horizontal proximal tibiofibular joint and tilted distal talofibular articular surface, robust interosseous membrane, broad malleolar fossa, projecting m. biceps femoris insertion) indicate greater mobility of fibular joints and load sharing during ankle and knee excursion in foraging groups, which are presumably highly active, frequently traversing uneven terrain with absent/minimalist foot coverings. Stiffer fibular joints (e.g., obliquely oriented tibiofibular and vertical talofibular articular surfaces) are observed in sedentary populations, which may suggest a restricted ankle excursion and limited lower limb loading and use, consistent with their sedentary lifestyle in plain urban settlements with hard-shoe coverings. Other fibular traits (e.g., shorter subcutaneous triangular surface, projecting and anteriorly-facing malleolus, concave peroneal groove and proximal peroneal insertion) might indicate for mobile groups a more everted foot posture with increased moment arm in eversion, more efficient for barefoot/minimal footwear running in a forefoot-strike gait and concurring in the stabilization of the first metatarsophalangeal ray. These results further stress the functional role of fibular morphology and its importance in studies investigating past population mobility patterns.