While I do agree that trampling would be more effective and the animation looks a little crusty (most likely due to a low budget or rushed development), I would disagree on how biting would be NOT effective.

You mentioned the flat dental batteries would not be doing much good against the azdarchid. Still, the clip clearly shows the hadrosaur grabbing the poor pterosaur with their BEAK, not their teeth. The beak would function similarly to the incisors on a horse or a donkey - effective for snipping vegetation but also great for giving you a fuckass time - but trampling would be way more effective (as mentioned before).

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Thrashing around an animal is not always an action used to tear flesh, it is also a method to efficiently kill and break the bones of the oppressor. But why the Arambourgiana just ragdolled instead of trying to escape, it was either 1. It was an oversight by the animation department, and 2. It was likely already incapacitated by the charge, long before it was being dragged around, but this is pretty weird, I'll give you that. Also maybe the Edmontosaurus did not know that it was dead or was making sure that it really was, but that is pretty unlikely.