title: Anatomy of Shoulder Girdle Muscle Modifications and Walking Adaptation in the Scaly Chinese Pangolin (Manis Pentadactyla Pentadactyla: Pholidota) Compared with the Partially Osteoderm-Clad Armadillos (Dasypodidae).
abstract: Because pangolins are unique mammals with a body and limbs almost entirely sheathed in hard keratinous overlapping scales and with digging and climbing abilities, the shoulder girdle muscles may differ significantly from those of other mammals including the partially osteoderm-clad armadillos. Therefore, we conducted a functional anatomical study of the shoulder girdle muscles in Chinese pangolins (Manis pentadactyla pentadactyla, Pholidota) and some armadillo species (Dasypodidae). Our CT scans revealed that the pangolin's overlapping scales are hard structures completely encasing the limbs. The armadillo's limbs, however, are covered with small relatively soft non-overlapping scales embedded in the skin, and articulate completely free of the hard osteodermal carapace. The attachments of some shoulder girdle muscles in the pangolin have moved from the surrounding edges of the scapula to the spine, and they, therefore, fully cover the scapula. In addition, some pangolin shoulder girdle muscles cross the shoulder joint to insert on the distal humerus, but this does not occur in armadillos. We cannot rule out the possibility that these muscle modifications represent adaptations for digging and/or climbing in pangolins. Our results and previous literature do not establish specific links between them and locomotive modes. However, we propose that the Chinese pangolin may use its derived muscular features when walking to move its armor-restricted forelimbs more effectively by swinging its head from side to side.
authors.affiliation: Department of Anatomy, School of Medicine, Toho University, Tokyo, Japan.
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Kawashima
authors.affiliation: Division of Mammals, Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, District of Columbia.
authors.forename: Richard W
authors.initials: RW
authors.lastname: Thorington
authors.affiliation: Division of Mammals, Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, District of Columbia.
authors.forename: Paula W
authors.initials: PW
authors.lastname: Bohaska
authors.affiliation: Division of Bird and Mammal, Department of Zoology, National Museum of Natural Science, Taichung, Taiwan.
authors.forename: Yen-Jean
authors.initials: YJ
authors.lastname: Chen
authors.affiliation: Department of Anatomy, School of Medicine, Toho University, Tokyo, Japan.
authors.forename: Fumi
authors.initials: F
authors.lastname: Sato
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D001135:Armadillos / Q000033:anatomy & histology / Q000502:physiology; D008322:Mammals / Q000033:anatomy & histology* / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000502:physiology; D012782:Shoulder / Q000033:anatomy & histology* / Q000502:physiology; D016138:Walking / Q000502:physiology*
keywords: armadillo; evolutionary morphology; functional anatomy; imaging analysis; locomotion; pangolin; shoulder girdle muscles