Functional morphology and three-dimensional kinematics of the thoraco-lumbar region of the spine of the two-toed sloth.
Given the importance of thoraco-lumbar spine movements in the locomotion of mammals, it is surprising that in vivo three-dimensional (3-D) data on the intervertebral movement of the mammalian thoraco-lumbar vertebral column during symmetrical gaits is limited to horses and dogs. To test whether kinematic patterns similar to those published for these cursorial species are also present during a contrasting mode of quadrupedalism, we quantified thoraco-lumbar intervertebral movements, the resulting pelvic displacements and relative femoral movements during the trot-like steady-state suspensory quadrupedal locomotion of the two-toed sloth (Xenarthra, Choloepus didactylus). Scientific rotoscoping, a new, non-invasive approach that combines synchronous biplanar high speed X-ray videos and the reconstruction of skeletal elements from computed tomography bone scans, was used to quantify 3-D kinematics. An analysis of vertebral anatomy and epaxial muscle topography suggests that the thoraco-lumbar spine of sloths is well suited to producing lateral bending and long-axis rotation, but limits powerful sagittal extension. Sloths exhibit complex 3-D movements in the thoraco-lumbar spine that are comparable to those observed in other arboreal quadrupedal mammals. Monophasic lateral bending and long-axis rotation, biphasic sagittal bending and maximal amplitude of sagittal bending at the lumbo-sacral joint were also found in other quadruped mammals and may represent general aspects of mammalian symmetric gaits. Maximal amplitude of lateral bending and long-axis rotation vary in regard to the vertebral level. It is suggested that a cranio-caudal pattern of angular deflections of the spine results from the out-of-phase movement of diagonal forelimbs and hindlimbs in other walking gaits, because it is not evident in the trot-like locomotion analyzed here. The analysis also illustrates the difficulties that arise when lumbar movement is deduced from intervertebral joint morphology alone.
Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universität, D-07743 Jena, Germany. john.nyakatura@uni-jena.de
John A
JA
Nyakatura
Martin S
MS
Fischer
D000818:Animals; D001696:Biomechanical Phenomena; D005269:Femur / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology; D006614:Hindlimb / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology; D021621:Imaging, Three-Dimensional; D008124:Locomotion / Q000502:physiology*; D008159:Lumbar Vertebrae / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology*; D010388:Pelvis / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology; D011859:Radiography; D012896:Sloths / Q000033:anatomy & histology / Q000502:physiology*; D013904:Thoracic Vertebrae / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology*