Meeting Abstract

P3.58  Tuesday, Jan. 6  Loading patterns of the femur in opossum ( Didelphis virginianis ) during terrestrial locomotion BUTCHER, M.T.*; PARRISH, J.H.A.; BLOB, R.W.; Youngstown State University; Clemson University; Clemson University mtbutcher@ysu.edu

Previous studies have found that mammalian limb bones typically are loaded predominantly in bending with minimal torsion, whereas the limb bones of non-avian reptiles (and amphibians) experience considerable torsion in addition to bending. However, most data on limb bone loads for mammals have been collected from large or cursorial species (e.g., horses, dogs, sheep) in which the limbs tend to be held upright. To better clarify the evolutionary timing of the distinctions in bone loading patterns between reptiles and mammals, we measured in vivo terrestrial locomotor strains in the femur of the Virginia opossum (Didelphis virginianis), a marsupial that uses more crouched limb posture than previous mammals from which bone strains have been recorded, and which belongs to a clade phylogenetically between reptiles and the eutherian mammals studied previously. If limb bone loading patterns in opossum show torsion similar to amphibians and non-avian reptiles, then the patterns shown across these diverse taxa likely reflect the ancestral condition of tetrapod limb bone design. Strain recordings indicate the presence of both bending and a moderate amount of off-axis loading in the opossum femur, suggesting elevated limb bone torsion compared with most previously studied mammals. Supported by NSF I0B-0517340.