For 135 million years during the Mesozoic the elongate-necked plesiosaurs lived in the oceans around the globe. Using 3D modeling, comparative anatomy, and soft tissue reconstruction I estimated the neck mobility of the plesiosaur, Nichollssaura borealis. I produced a series of 3D models of the cervical vertebral column from computed tomography scans of N. borealis. To quantify the range of motion, the intervertebral mobility was measured along the cervical vertebral column by manipulating the 3D models in the dorso-ventral and medio-lateral planes. The neck moves most in the lateral plane up to a maximum mean intervertebral mobility of 13.51˚ (+/-1.113˚). Extant phylogenetic bracketting was used to reconstruct and map the hypothetical musculature onto the preserved morphology of N. borealis. The hypothesized soft tissues show that musculature used for medio-lateral movements may have dominated in N. borealis. Studying N. borealis’s neck mobility allows us to understand plesiosaur prey captures abilities, hydrodynamics.