Little Red Riding Hood had it right.
Whenever something is out of the ordinary, like big teeth on ‘Grandma-ma’, we take notice.
Most pterosaurs have gracile gastralia, those boomerang-shaped bones that cover the belly of pterosaurs and many other reptiles. The most obvious exception is Nyctosaurus, in which the gastralia are quite robust and for good reason.
While all pterosaurs had to support the long lever arm of their upper/anterior selves at the fulcrum of the lumbar/sacral series interface, perhaps no pterosaur had quite the imbalance of forces seen in Nyctosaurus, with its long metacarpals and rostrum. In any case, Nyctosaurus developed a strong ventral basket of robust gastralia to prevent rotation of the lower lumbar area, which would have acted to shorten the distance between the sternum and prepubes in Nyctosaurus. I learned about this mechanical problem while building a full scale Nyctosaurus model based on UNSM 93000 (skull largely unknown, Fig. 2).
Quadrupedal Pterosaurs Avoided This Problem
Whether you support yourself with long metacarpals, long antebrachia or long ski poles, the stress on the lower back goes away and you don’t need to develop such robust anti-rotational supports in your belly. And of course, the whole problem goes away when you are airborne and supporting yourself by lift from both wings and thighs.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.