Mantle has a posterior suture.
Independent evolution of parts is well shown among invertebrates, where the shell of an ammonite, for example, may change markedly in form without a corresponding change in suture, or vice versa.
The pressure a growing brain exerts on a fused suture also can cause a delay in development or, rarely, permanent brain damage.
Jimenez, David, et al. "Endoscopy-assisted wide-vertex craniectomy, barrel stave osteotomies, and postoperative helmet molding therapy in the management of sagittal suture craniosynostosis."
The vertebrae are stereospondylous, the centrum or body and the arch being com pletely fused into one mass, leaving not even a neuro-central suture.
