Dragons can have different types of scales on different parts of their bodies. I learned this from the excellent dragon-drawing book, "Dragonart: Evolution" by J. "Neondragon" Peffer. This is the sequel to her original dragon book, "Dragonart," which I used as a model to educate myself in dragon drawing. "Evolution" is full of dragon drawing builds that I can follow to learn more. I'm also learning more about digital inking, which is commonly used in comic book art these days. One thing I just learned is that drawing too many small lines (for cross hatching, pen shading, etc.) confuses Photoshop and your computer so badly that your computer, no matter how powerful, fails and seizes up and you lose the part of your drawing that you didn't save. I guess that is a win for the old fashioned hand penmanship. There is no law that says you can't do both kinds of drawing. This image here is a hybrid, containing both pen and digital drawing. Until the computer seized, you couldn't tell the difference.
Ink drawing on sketchbook page, augmented by digital inking in Photoshop, 6" x 5", April 19, 2013.