CONCLUSIONS

That the shape of the carnivoran calcaneum is related to locomotor function comes as no surprise. The mammalian ankle joint is well-studied and the relation of form and function well-understood (Jenkins and McClearn 1984; Szalay 1977, 1994; Taylor 1970, 1976, 1988, 1989). But quantitative functional analysis of tarsal bones has not been as successful as it has with limb proportions or humerus, ulna, or radius shape (e.g., Andersson 2004; Andersson and Werdelin 2003; MacLeod and Rose 1993; Van Valkenburgh 1985) because the functional features of tarsals are the curved surfaces of their interlocking joints.

The success of our 3D eigensurface method, while qualified, is encouraging. Eigensurface analysis of the 3D topography of calcanea sorted them into the same functional spectrum that qualitative functional analysis would have. Importantly, the quantitative descriptors of calcaneum shape allowed fossil calcanea to be assigned to the functional categories of stance, digit number, and locomotor style nearly as accurately as was possible through qualitative functional analysis of the entire postcrania. The general agreement of our quantitative results with previous qualitative assessments of locomotor function in four extinct carnivorans suggests that isolated calcanea, which are comparatively common in the mammalian fossil record, could be interpreted functionally with nearly the same degree of confidence as we now place in interpretations based on complete limbs.