Step 10: Use the initial thin, long arc as a guide to draw the mosasaurus' muzzle. Follow the basic path of the arc but make the shape bumpier as you darken the line. Make the bottom part bumpy too, especially where the mouth meets the teeth. Add a few lines above the teeth to give the dinosaur's skin extra rough texture.
Step 11: Use the arc on the bottom as a guide to draw the mosasaurus' lower jaw. Make the top line less bumpy than the head but a bit more wavy. Make the bottom line wavy too and add an extra curved line on the right for the skin folds.
Step 12: Add a row of small triangle-like shapes across the mosasaurus' bottom jaw for the teeth. Space the teeth apart and add a few lines below them within the jaw to give the skin more texture.
Step 13: Draw a few short vertical lines for the bit of skin that connects the mosasaurus' jaws. Add a couple of curved lines above the teeth for the tongue and the other side of the jaw. Draw a series of small triangle- like shapes on top of the curved line for the teeth on the other side.
Step 14: Add a series of lines within the shape of the mosasaurus' head to give the skin more texture. Add some lines to the right of the eye to emphasize the shape of the cranium. Don't overdo it with the lines, otherwise they'll start to look like fur. Add some at the bottom too.