Why is vertebral pneumaticity in sauropod dinosaurs so variable?

The vertebrae of sauropod dinosaurs have distinctive and complex pneumatic features including fossae foramina in the sides their centra. These vary between individuals, serially within even left right single vertebrae. This presents a conundrum because bone is usually least variable material vertebrate body. Blood vessels, however, are much more labile, as can be seen varied occurrence vascular not only sauropods, but also birds, crocodilians mammals. Vascular variation arises part from ontogeny vertebrae, which embryonic state vascularised neural canal: hand-off these vessels to others penetrate outside always completed. In pneumatizing diverticula enter alongside blood that they form, before excavating surrounding into larger foramina. We propose same was true vascularization directly caused pneumatization. most foramen carries both artery vein, occasionally separate each forms foramen. explains why rare cases individual two cavities on side: formed by either or vein.