Theropods and lips

Problem:
Many predators protect their teeth from corrosion caused by air using lips, yet there was a new study published stating theropod dinosaurs from the tyrannosaurid family do not appear to have had them.

Short answer:

No lips anymore.

Long answer:

First of all the new discovery. The researchers certainly haven't put the claim "no lips" in the title... I know this isn't a strong argument just sain'

Secondly: using living relatives and a nearly realated group. Both living relatives, birds and crocodiles, do not have lips. Bird have toothless beaks, not in the need of protecting any teeth, and crocodiles  simply don't have lips, being semi-aquatic creatures. However,  there is a group of mostly carnivorous, fairly near realated creatures which do have snouts as well as beaks, and teeth in both of them: pterosaurs. We found soft tissue in all forms and shapes on them, from pulmonary airsacs to wing membranes, fuzzy integument and even head crests with preserved colouration, yet we found not one of them with lips, but even contrary: Pterodactylus shows teeth as well as a ceratinous sheath, not protecting the teeth, even though it was a flyer and was moving through the corrosive air with big speeds, even foraging in much more corrosive salt water for little grubs. Same goes for Rhamphorhynchus, which lived in the same time at the same place, though belonging to a different family of pterosaurs. It was a piscivore adapted to catch fish offshore using impressive maneuvers. If these gracile flying creatures  managed to keep their teeth safe from environmental damage, and did so under much harsher conditions without the use of lips, I believe it is safe to say that theropods could as well.

Please share this, I wanna see an active, open-minded, public discussion :3