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CONCLUSIONSThe presence of vertebral pneumaticity in the neck of sauropods can be reconstructed based on osteological evidence and by comparison with extant birds. Depending on the overall size and distribution of pneumatic diverticula, there are sauropods with a dual pneumatic system and sauropods with a tripartite pneumatic system. Whereas the osteological evidence for the size of the cervical pneumatic diverticula is restricted to pneumatic fossae and foramina on the cervical vertebrae, the comparison with extant birds suggests an expansion of diverticula systems beyond their bony frame. Different extensions of the pneumatic diverticula in the sauropod neck can be reconstructed, ranging from a minimum to a maximum expansion model. These differences in the reconstructed size of the cervical diverticula systems influence a possible pneumatic support function of the cervical pneumatic apparatus in sauropods. Integrating vertebral pneumaticity in a model of neck support for sauropods shows that pneumatic diverticula could not achieve bracing of the neck alone. However, pneumatic support mechanically coherent with other bracing structures yields a model for the neck support in sauropods that is consistent with anatomical development of non-pneumatic bracing structures. As shown in the experiment, the interaction of pneumatic support with other bracing elements increases the support effect of the whole system, but only if all systems are coherent. Thus, integrating pneumaticity into neck support might explain, why sauropods could develop such elongate necks for their large body size. Judging from a functional basis, pneumatic support in sauropod necks therefore would be an option to stabilize a long neck effectively at low weight. Experimental data with a simplified chain beam model show that a support function of pneumatic systems, with a configuration modelled after sauropod constructions, would be possible. Preconditions for such a pneumatic support are (1) that pneumatic diverticula extended beyond their bony boundaries, and (2) that regulation mechanisms for pressure maintenance and control in the air sac systems were present. Because of those preconditions neither the exact expansion of the cervical pneumatic system, nor regulatory mechanisms and the height of pressure in these pneumatic systems can be demonstrated on osteological evidence, the pneumatic support of sauropod necks remains hypothetical. With osteological evidence as a measure, the question of a mechanism of pneumatic support of sauropod necks must therefore remain unresolved at the moment, which holds true for any physiological assumptions concerning the respiratory system. |
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