John A. Fronimos & Jeffrey A. Wilson (2016)
Neurocentral suture complexity and stress distribution in the vertebral column of a sauropod dinosaur.
Ameghiniana (advance online publication)
Sauropod dinosaurs achieved extreme body sizes via rapid and sustained growth, permitted in part by the delayed fusion of the neurocentral sutures. Unfused sutures are joined by cartilage, which is more susceptible to dislocation than the bone that replaces it. In sauropods, the competing interests of growth and strength were balanced by the presence of complex, interdigitated neurocentral sutures. Sutural complexity is correlated with the magnitude of stress the suture must resist. To better understand this relationship in sauropods, sutural complexity was measured from the articulated presacral vertebrae of Spinophorosaurus nigerensis, and patterns of gross morphology were observed. Complexity was calculated as a length ratio and as the fractal dimension of the suture. The complexity pattern indicates that stress increased proximally along the neck, was greatest in the anterior dorsal vertebrae, and then decreased towards the sacrum. This stress distribution is attributable to the weight of the neck and the ribcage. The sutural structures are oriented to resist anteroposterior translation of the neural arch in cervical vertebrae and lateral rotation in dorsal vertebrae. This pattern could result from the greater mechanical advantage of an elongate cervical centrum in resisting torsion relative to a short dorsal centrum and the greater mechanical advantage of wide dorsal transverse processes in generating torsion. The patterns and structures described are similar to those of Alligator. Complex neurocentral sutures may represent an archosauriform adaptation that facilitated rapid growth rates and large adult body sizes.