Ancient tetrapods evolved a diverse array of complex vertebrae 360 million years ago. These complex vertebrae—composed of separate non-fused elements, or persistent notochords—were ubiquitous in every major stem tetrapod lineage. Nevertheless, paleobiologists have struggled to come to a consensus on the role of complex vertebrae on single vertebral joint range-of-motion (ROM), and in turn, overall spinal flexibility. This disagreement is in part due to the difficulty of modeling multipartite forms. Additionally, only three families of extant animals (Lacertidae, Xantusiidae, Gekkonidae) have complex vertebrae, the homology of their vertebral elements, and applicability as modern analogs to understanding stem tetrapod vertebrae remain unknown. However, with advances in 3D digital modeling and printing, modeling complex vertebrae with fidelity are now possible. To estimate vertebral ROM and passive stiffness in ancient tetrapods, we used both 3D virtual models and printing to investigate the form-function relationships of single intervertebral joints in five well-preserved and understood ancient tetrapods. These taxa represent different habitats, vertebral forms, and maximum sizes. We hypothesized that multipartite vertebrae would have greater ROM than taxa with fused elements but persistent notochords(monospondylous). Contrary to expectations, we found complex vertebrae have smaller ROM than monospondylous vertebrae. Conversely, we find stiffness is related to habitat, not vertebral composition. Finally, our results showed linear and angular measurements that are correlated with vertebral ROM in extant taxa are not correlative in our Permian taxa, demonstrating a need for more empirical studies.