Reasons for lips: Many dinosaurs appear to have pitting along their jaw line that appears homologous to the pitting that anchors the lip tissue of lizards. Enamel is stronger when it is kept moist. Exposed enamel can grow brittle or get infected. Crocodiles have a certain enamel wear pattern from having exposed teeth that we don't see in dinosaur tooth fossils. Some theropods have fairly long tooth 'lifespans' before replacement. Any damage to a tooth could be very problematic. Ornithischian dinosaurs are assumed to have had cheek pouches. Multiple theropod lineages are secondarily herbivorous and likely had cheek pouches. This would have had to have been developed independently. Some theropod dinosaurs may have had difficulty closing their mouths fully because of their tooth size. Lips would cover this.
Reasons against lips: Lizards are not closely related to dinosaurs and are not often used as analogs in other situations. Neither crocodiles nor birds have lips. Some say that the pitting pattern found on theropod faces is not as lizard-like claimed. Certain species of theropods clearly had dental arrangements like interlocking teeth that would not have possible with lips. They would have had to evolve to not have lips. Uncrushed theropod skulls have been found that are comfortably fully closed without damage. Some theropod skulls appear to have recesses in the top of the mouth that would accommodate teeth. Theropod tooth wear patterns don't indicate that they would have even rubbed on one another. Theropod mouths are generally very large.
Did I miss anything?
00
Anonymous06/11/26(Thu)20:33:56
No lips or skin or flesh. Dinosaurs were always skeletons.