But even though dinosaurs likely didn't have things like trunks hanging off their faces, there are plenty of questions about how they looked. One important question is how well dinosaurs could kiss. Like, did they have lips? Robert Bakker and other paleontologists are associated with promoting the idea that dinosaurs had fleshy lizard lips:
The prolific and inspirational dinosaur artist Gregory S. Paul also illustrated dinosaurs with lips. Though I used to illustrate dinosaurs with lips, I no longer do. Amateur paleontologist Tracy Ford and others have promoted the idea that maybe dinos lacked lips. One argument is that the lips of lizards are formed by scales growing over and past glands that are found just above the gumline on the outsides of their skulls. Since dinosaurs (probably?) didn't have these glands, or overlapping scales, why would they have grown lips? Paleontologist Lawrence Witmer and his research lab are important go-to guys about the soft tissue of dinosaurs. He has been interviewed about the subject and questions whether any dinosaur had any muscular cheeks or any fleshy mouth structures. The point is that crocs don't have lips, and birds might not have lips, and since they are dinosaurs' closest relatives, why not check them out for their facial structures? Why not, I ask you?
So lips are gone. But what kind of flesh covering did the jaw attachment site have? Gregory S. Paul drew his dinosaurs' jaw attachments with a very revealing lizard-like sheet of skin covering the musculature along with their lips.
(detail from here):As compared to this lizard: Once I took lips off their faces, I wasn't sure the sheet of skin made sense any more. Here's a crocodile:
Crocs' facial skin is very highly adapted to their sensory and lifestyle needs. Their skin tightly follows their skulls' contours, and at the ears and nostrils they have evolved very specific structures suitable to their semi-aquatic lifestyles. Are their jaw attachment sites similarly specialized for croc lifestyles, or more accurate for dinosaurs? I followed their example in the drawing of T. rex at the top of the page (also here) and in this drawing of Coelophysis bauri:
Then one day I had the chance to stick my finger in some predatory birds' mouths. That was cool. I got to know a falconer who brought out his birds and let me actually touch the beaks and claws of his falcons and hawks. Then I got to draw from them and study frozen bird carcasses. That was fun for me, though some wouldn't prefer it to an afternoon, of, say, cow-tipping. Hawks have a tough skin that hides all of their jaw musculature:
Other birds have a similar structure, albeit a bit more revealing:
So in the spirit of scientific experimentation (in art), I chose to draw bird-like cheeks and no lips on these guys.
But the ultimate answer is that we don't, and won't, know for sure. Soon I'll explain why T. rex may not have had the cheek structure I drew, despite my best efforts. Until then, here's a crazy dinosaur with, in this case, lips. Heeeere's Suchomimus tenerensis: