On pterosaur neck vertebrae (Patreon)

Kren pakshee, a fictional nyctosaurid from Nyctosaurid Earth. The original description had this and it's ilk have more neck vertebrae than the azhdarchids they mimick, but it has since been rectified.

One thing that I see neglect is how pterosaurs seem to have a limited amount of neck vertebrae. Whereas other reptiles have a wide range of cervicals, pterosaurs invariably have seven (Wellnhofer 1991, Witton 2013); to acquire longer necks, groups like azhdarchids and ctenochasmatoids elongated their cervicals, resulting in long but inflexible necks.

This is coincidentally the same number of vertebrae mammals are restricted to (manatees and a few others nonwithstanding). Given that the limited number of mammalian neck vertebrae is dictated by genetic modules, that render anomalies with more than seven cervicals subject to cancer (except for forms with slow metabolism, like the aforementioned sloths and manatees), I wonder if pterosaurs were subject to similar modules.

Notably, pterosaurs have proportionally large heads, much like mammals. This might imply that they faced similar biomechanical pressures in terms of supporting their head. And since they all had high metabolisms, they wouldn't be able to get away with more or less neck vertebrae.

Hopefully more studies will illuminate this situation.