PATEL, BIREN, A.*; CARLSON, KRISTIAN, J.; Stony Brook University; Universitat Zurich – Irchel: Subchondral bone mineral density in the distal radius reflects habitual use of the forelimb in sloths and anteaters (Order Xenarthra)

Estimates of in vivo joint load history can be made from articular surfaces because bone mineral density is directly proportional to the compressive strength of bone. Subchondral bone experiencing greater compressive loads should exhibit relatively greater mineralization than subchondral bone experiencing less compressive loading. While this has been demonstrated in this distal radius of a wide range of primates, it is unclear whether this is a taxon specific trend (i.e., Order Primates), or whether it is more generalized among mammals. We examined patterns of subchondral bone mineralization in the distal radius of three families of the Order Xenarthra. The Megalonychidae and Bradypodidae (sloths), which are suspensory groups that load their forelimbs in tension were compared to the Myrmecophagidae (anteaters), which are quadrupedal and load their forelimbs in compression. Computed tomography osteoabsorptiometry (CT-OAM) was employed to acquire digital data from which subchondral mineralization patterns of the distal radial articular surface were assessed. Optical densities were measured in order to construct false-color maps that were used to evaluate mineral density patterns. Suspensory sloths had smaller percentage areas of high mineral density regions relative to quadrupedal anteaters, as was the pattern observed in suspensory and quadrupedal primates. A significant difference between groups characterized by predominantly compressive loading regimes (i.e., quadrupedal) versus predominantly tensile loading regimes (i.e., suspensory) supports previous results that subchondral mineralization in the distal radial articular surface can be used to distinguish forelimb involvement in the habitual support of body mass.