One of the main evolutionary trends in pterosaurs is the reduction of teeth. Clearly, where teeth are not essentially required for feeding, a reduction in teeth numbers would be a weight saving factor, giving some pterosaurs a survival advantage.
The first noticeable reduction in teeth came with some of the species that only retained teeth at the end of the jaw.
It seems likely that any pterosaur that had teeth in the anterior jaw only, would need cheek pouches to stop food falling out of its mouth. There is no evidence for this in the fossil record.
The function of the bony crest is unclear, but it is likely to serve as a jaw strengthening structure and possibly a display crest. If Tapejara was a water feeder, then this may also be an aqua-dynamic stabilising structure.
Examples of complete tooth reductions can be seen in the jaws of the giant pterosaurs; Nyctosaurus, Pteranodon and Azhdarcho, where the smooth beak like jaws have no teeth at all.
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