Helically arranged cross struts in azhdarchid pterosaur cervical vertebrae and their biomechanical implications

Abstract

Trabeculae in a pterosaur cervical vertebra are helically arranged.As few as 50 trabeculae increase the buckling load by up to 90%.

The absence of an invasive air sac system in the earliest dinosaurs suggests multiple origins of vertebral pneumaticity

“…Those latter must also be connected with clear internal pneumatic architecture 3 , 30 , 41 . Most pneumatic vertebrae are internally organized into camerate and camellate bone tissues, and these are the best macroscopic correlates of bone-penetrating pneumatic diverticula 11 , 13 , 29 , 36 , 37 , 42 , 43 . These Carnian taxa failed to show an architecture consistent with pneumatization, such as that observed in the derived sauropods Saltasaurus (PVL 4017–17/214) 11 and Ibirania (LPP-PV-0200) 37 , and theropods like Aoniraptor (MPCA-Pv 804/1-25) 43 and noasaurids (DGM 929-R) 36 .…”

Quantitative assessment of the vertebral pneumaticity in an anhanguerid pterosaur using micro-CT scanning

“…The mean ASP for each vertebra of SNSB/BSPG 1991 I 27 varied between 68 and 72%. Furthermore, we observed here a reduction of the ASP and increase in the area occupied by trabecular bone in the cranio-caudal direction in the vertebral series of SNSB/BSPG 1991 I 27, which may be related to a biomechanical requirement of the vertebral column 36 , 37 , 48 – 50 . Within the same vertebra, ASP values in the neural arch were higher at mid-length and decreased towards the zygapophyses, indicating a probable need for a higher level of stiffness 44 .…”

“…The lower ASP values of the cotyle and condyle compared to those of the zygapophyses possibly indicate a more rigid articulation in the centrum. The sixth cervical is the exception, as it presented the most pneumatised cotyle and condyle of all analysed vertebrae (Table 2 ), suggesting that the support for resistance in the joints of the centrum of the middle cervical vertebrae probably require less of the presence of trabecular bone than in the posterior vertebrae 37 .…”

“…3 ). The increase in the proportion of trabecular bone in the centrum may be a biomechanical requirement to guarantee structural integrity and to confer more resistance to withstand the stresses caused by the movements naturally exerted by the base of the neck 35 , 36 , since the increase in trabeculae tends to increase elastic stability 37 .

Figure 3 The internal architecture of trabeculae in the mid-length of the vertebrae .

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“…In any case, the variation in pneumaticity presented here suggests a pattern of reduced pneumatisation in the cranio-caudal direction and a decrease between zygapophyses in relation to the neural arches. Therefore, we hypothesise that the quantitative disposition of the air space follows a pattern that may be related to the biomechanics of the neck 37 .The mean ASP per vertebra of SNSB/BSPG 1991 I 27 (range 0.68–0.72; median: 0.705) was lower than the value (0.83) presented for an indeterminate azhdarchoid cervical vertebra fragment stored at the Staatliches Museum für Naturkunde Karlsruhe, Karlsruhe, Germany, SMNK 3985 22 . However, the analysed cross-section seems to belong to the middle part of the neural arch, which data collected here shows to be more pneumatised than the centra.…”