Introduction

Among the extant mammals, primates display a great diversity of postural and locomotor behaviours. In an evolutionary perspective, this variation relates to their adaptive ability to exploit a full range of arboreal and terrestrial substrates (Jouffroy et al., 1990; Hunt et al., 1996). Principal primate locomotor modes include arboreal and terrestrial quadrupedalism, vertical clinging and leaping, saltation, suspensory climbing, brachiation, knuckle and fist-walking quadrupedalism, and bipedalism (Gebo, 1996). These varied locomotor patterns result in specific types of limb use which rely on a number of anatomical and biomechanical musculoskeletal specialisations (Conroy, 1990; Fleagle, 1999).

Following the principle of uniformitarianism, the reconstruction of body postures and modes of locomotion in fossil taxa is primarily based on the comparative analysis of external bone shape, size and proportions with the respective skeletal elements of living forms. Despite its obvious – but inescapable – intrinsic limits (Preuschoft, 1975), correlations between bony morphology and positional/locomotor behaviours ‘are constantly being tested and refined by experimental studies that permit a clearer understanding of the biomechanical and physiological mechanisms of primate evolution’ (Fleagle, 1999: 298).

In the last few years, there has been a growing interest for potential functional analysis and interpretation of fossil trabecular bone patterns, a previously underexploited tool for various aspects of vertebrate paleobiology. As ‘living bones modify their structure at gross, tissue, and molecular levels in response to the force patterns acting on them … the preserved structure of fossil bones may contain direct information on the forces that may have been experienced during life’ (Thomason, 1995: 249).