title: Vertebral bending mechanics and xenarthrous morphology in the nine-banded armadillo (Dasypus novemcinctus).
abstract: The vertebral column has evolved to accommodate the broad range of locomotor pressures found across vertebrate lineages. Xenarthran (armadillos, sloths and anteaters) vertebral columns are characterized by xenarthrous articulations, novel intervertebral articulations located in the posterior trunk that are hypothesized to stiffen the vertebral column to facilitate digging. To determine the degree to which xenarthrous articulations impact vertebral movement, we passively measured compliance and range of motion during ventroflexion, dorsiflexion and lateral bending across the thoracolumbar region of the nine-banded armadillo, Dasypus novemcinctus Patterns of bending were compared with changes in vertebral morphology along the column to determine which morphological features best predict intervertebral joint mechanics. We found that compliance was lower in post-diaphragmatic, xenarthrous vertebrae relative to pre-xenarthrous vertebrae in both sagittal and lateral planes of bending. However, we also found that range of motion was higher in this region. These changes in mechanics are correlated with the transition from pre-xenarthrous to xenarthrous vertebrae, as well as with the transition from thoracic to lumbar vertebrae. Our results thus substantiate the hypothesis that xenarthrous articulations stiffen the vertebral column. Additionally, our data suggest that xenarthrous articulations, and their associated enlarged metapophyses, also act to increase the range of motion of the post-diaphragmatic region. We propose that xenarthrous articulations perform the dual role of stiffening the vertebral column and increasing mobility, resulting in passively stable vertebrae that are capable of substantial bending under appropriate loads.
authors.affiliation: Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA spierce@oeb.harvard.edu jillian_oliver@brown.edu.
authors.forename: Jillian D
authors.initials: JD
authors.lastname: Oliver
authors.affiliation: Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Katrina E
authors.initials: KE
authors.lastname: Jones
authors.affiliation: Institut des Sciences de l'Evolution, UMR 5554, CNRS, IRD, EPHE, Université de Montpellier, 34090 Montpellier, France.
authors.forename: Lionel
authors.initials: L
authors.lastname: Hautier
authors.affiliation: Department of Biology, Valdosta State University, Valdosta, GA 31698-0015, USA.
authors.forename: W J
authors.initials: WJ
authors.lastname: Loughry
authors.affiliation: Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA spierce@oeb.harvard.edu jillian_oliver@brown.edu.
authors.forename: Stephanie E
authors.identifier: 0000-0003-0717-1841
authors.initials: SE
authors.lastname: Pierce
mesh_terms: D000818:Animals; D001135:Armadillos / Q000033:anatomy & histology* / Q000502:physiology*; D001696:Biomechanical Phenomena; D002138:Calibration; D003187:Compliance; D008159:Lumbar Vertebrae / Q000033:anatomy & histology* / Q000502:physiology*; D025341:Principal Component Analysis; D016059:Range of Motion, Articular; D013904:Thoracic Vertebrae / Q000033:anatomy & histology* / Q000502:physiology*
keywords: Biomechanics; Dasypodidae; Locomotion; Morphology; Vertebral column; Xenarthra