Meeting Abstract

74.2  Tuesday, Jan. 6  Primitive, Protected and Pendullar: Locomotor Dynamics of Echidnas and Hedgehogs BIKNEVICIUS, A.R.*; MCELROY, E.J.; JOHNSON, S.D. ; BENNETT, M.B. ; REILLY, S.M. ; Ohio University College of Osteopathic Medicine, Athens; College of Charleston, South Carolina; University of Queensland, Gatton, Australia; University of Queensland, Brisbane, Australia; Ohio University, Athens biknevic@ohio.edu

When small terrestrial mammals travel at steady speeds they predominately move their center of mass (COM) in a manner consistent with spring-mass (running) mechanics. In order to determine whether this is a primitive condition in mammals, we investigated COM mechanics in echidnas (Tachyglossus aculeatus) and hedgehogs (Atelerix albiventris). The skeletons of both species have a suite of characters that have been considered by some to be primitive for the Mammalia. While the gait used by both species at slow speeds was typically either a lateral-sequence (LS) diagonal-couplet or LS singlefoot, speed-related gait changes differed between species; Atelerix shifted toward the trot and Tachyglossus tended toward the pace. Across all speeds Tachyglossus moved exclusively with pendulum-like (walking) mechanics. This was also the principal mode in Atelerix, although hedgehogs were also capable of moving with spring-mass mechanics at higher speeds. These observations are in contrast to the predominantly running mechanics in other small mammals. Mammals with armored integument may not be under the same selective pressures as unarmored mammals; instead, they may have been selected to move customarily at moderate to slow speeds, relatively undisturbed, as they forage for widely distributed prey. Our observations support a hypothesis that the predominant use of spring-mass mechanics during steady speed locomotion in other small mammals may reflect their tendency to use flight-mode locomotor speeds for steady speed locomotion, more so than an inability to move with pendulum-like mechanics.