Meeting Abstract

P1.139  Monday, Jan. 4  Patterns of strain in the femur of the opossum ( Didelphis virginiana ) during terrestrial locomotion BUTCHER, M.T.*; HUDZIK, N.B.; WHITE, B.J.; WOLFF, L.M.; GOSNELL, W.C.; PARRISH, J.H.A.; BLOB, R.W.; Youngstown State University; Youngstown State University; Youngstown State University; Youngstown State University; Clemson University; Clemson University; Clemson University mtbutcher@ysu.edu

Previous studies have found that limb bones from upright, cursorial species of eutherian mammals experience high bending loads with minimal torsion, whereas the limb bones of non-avian reptiles exhibit considerable torsion in addition to bending. To help determine the evolutionary timing of this divergence in bone loading patterns, we measured in vivo terrestrial locomotor strains in the femur of the Virginia opossum (Didelphis virginiana). This species not only uses more crouched limb posture than cursorial mammals but, as a marsupial, belongs to a clade phylogenetically between reptiles and the eutherian mammals studied previously. The presence of substantial torsion in the femur of opossums, similar to non-avian reptiles, would suggest that this loading regime likely reflects an ancestral condition for tetrapod limb bone design. Strain recordings indicate the presence of both bending and moderate torsion in the opossum femur. Shear strains appear similar in magnitude to peak compressive axial strains, with opossum femora experiencing lower bending loads but higher levels of torsion compared with most previously studied mammals. Thus, loading patterns of opossum limb bones appear intermediate in some respects between those of non-avian reptiles and mammals. Supported by NSF I0B-0517340.