Armadillos, sloths, and anteaters belong to the mammalian lineage Xenarthra. One of the most unique features of the lineage is given away by its name, which translates to “strange joint.” The strange joint in question is found along and between the posterior thoracic and lumbar vertebrae, and consists of enlarged vertebral processes that articulate in a manner peculiar to this lineage. Xenarthrous articulations are considered an ancestral feature for the clade, but have been secondarily lost in glyptodonts and modern sloths, and are specialized to different extents in all other members of the lineage. These articulations are thought to have developed as adaptations to fossoriality early in xenarthran evolution, but the direct functional link between the morphology and the mode of locomotion has yet to be substantiated. In this study, we are conducting biomechanical analyses on ex vivo intervertebral joints, and are taking linear and 3D geometric morphometric measurements on μCT-scanned thoracic and lumbar vertebrae of the nine-banded armadillo (Dasypus novemcinctus). By measuring the stiffness and range of motion of the intervertebral joints and by correlating these parameters with the articular morphologies of the joints, we aim to assess the functional consequences of xenarthrous articulations. Ultimately, we seek to gain insight into how the evolution of the xenarthrous articulation has been shaped by locomotor pressures, and into how it defines vertebral regionalization of the xenarthran vertebral column.
Dasypus novemcinctus, the nine-banned armadillo