Limb joint surface areas and their ratios in Malagasy lemurs and other mammals.

Surface areas of humeral and femoral heads scale largely as a function of body size. However, differences in the relative sizes of these articular surfaces are correlated with differential joint mobility and force transmission through fore- and hindlimbs. They can therefore assist interpretation of the positional behavior of extinct species. In this paper, we document variation in ratios of humeral head surface area to femoral head surface area among extant primates and other mammals. We then examine a group of extinct primates: the subfossil lemurs of Madagascar. Many Malagasy lemurs, including some giant extinct species with very long forelimbs and short hindlimbs, have relatively small humeral heads and large femoral heads. We explore the adaptive implications of this pattern.