INVESTIGATING SPINAL COLUMN DYNAMICS IN A TERRESTRIAL PERMIAN HERBIVORE

Technological advances have allowed paleontologists to investigate the mobility of and generate locomotor hypotheses surrounding crown-tetrapods that roamed terrestrial environments throughout the late Paleozoic in previously impossible ways. The primary focus of this body of work has been quantitative investigations of appendicular skeletal mechanics during dynamic locomotion. However, our understanding of axial column dynamics in these crown tetrapods is still lacking. From this knowledge gap, we lack a complete understanding of these early tetrapods' locomotor abilities, which inform hypotheses on potential predator-prey interactions in Permian ecosystems. Previous studies have focused entirely on joint mobility in the axial column. However, these types of studies cannot capture the dynamic mechanical properties of the spine, which vary with respect to time scale and frequency during locomotor motion. Moreover, these studies focus on a single vertebral unit comprised of two centra and a single intervertebral joint, obscuring potential differences in behavior generated by multi-jointed vertebral models. To investigate the dynamic capabilities of the spinal column in ancient tetrapods, we used Stratasys PolyJet multi-material 3D printing and a custom-built bending machine to capture the range of material stiffness within tetrapod vertebral units to estimate bending stiffness, damping coefficient, and resilience during dynamic bending. We selected a large crown herbivorous amniote from the Permian era for this investigation. We found that in dorsoventral flexion, a multi-jointed model has a predictable behavior from a single-jointed model; however, in mediolateral flexion single-jointed and multi-jointed structures are not readily comparable. Additionally, we found mediolateral stiffness at all frequencies to be greater than dorsoventral stiffness. We anticipate that subsequent researchers will be able to use these data to build dynamic-legged models that investigate the spine's role in-situ during dynamic locomotor gaits. Our study advances the broader study of dynamic locomotion in terrestrial tetrapods.