I often see depictions of the larger therapod dinosaurs such as T Rex, Allosarus and such with the upper teeth extending over the lower lip and exposed. But I have noticed in photos that there seems to be holes running along the upper edge of the lower jaws. I was woundering if they might have had a lower lip that covered the upper teeth when the mouth was fully closed as in modern lizards. I like to draw animals, including dinosaurs, as accruately as possible.

Theropods were eating machines. Their teeth and jaw structure were designed for optimum ripping and tearing, therefore the tremendous over bite of steak-knife teeth. Bottom lips would hinder. Draw them as they are depicted which amounts to years of study coming to the conclusion that they were made that way for a purpose.

You might take note of crocodiles with their overbite and this animal hasn't changed much in a million years.