Step 20 (optional): For a cleaner look, erase as much as you can of the initial guide lines. Don't worry about erasing all of the guides. It's okay to leave some behind. Re-draw any final sketch lines you may have accidentally erased.
Final Step (optional): Add some shading to your pteranodon drawing to give it more dimension and volume. Pick the direction of the light source when shading so that the shadows are consistent with it. Don't worry too much about the shading if you're going to add more value to your pteranodon drawing.
You can add even more value throughout your pteranodon drawing for extra detail. Add the value lightly at first, then gradually build up to the level of darkness that you want. Nobody knows for sure exactly what pterosaurs looked like, so you can shade yours any way you'd like! For a spotted pattern line this one, simply use a darker value on certain sections of the pteranodon's body. For a simpler drawing, just add a single value to the entire body. Don't worry about shading too smoothly. The rough value gives the skin texture. Shading can be time-consuming, so be patient and take breaks. Remember to pause the "How to Draw a Pteranodon" video after each step to draw at your own pace.