Overlapping Scales
Snake skin is made up of a repeating pattern of overlapping scales. These scales come in a variety of shapes, sizes, and textures. For this sketch, I chose oblong, arched shapes. I begin by drawing a diagonal guide with a subtle curve to follow the flow of the snake's body. Using this guide, I draw each scale one by one. Then I add a bit of shadow where the scales overlap to create depth and realism.

Random Rectangles
Crocodilian skin has a rough, armored texture made up of irregular rectangular shapes. I start with a loose grid, placing smaller rectangles along the edges and larger ones toward the center. Each rectangle is uneven in size and shape. After outlining the pattern, I add shading to give the skin a three-dimensional look.

Irregular Geometric Patterns
Turtle shells are made of scutes, which are large, hard plates. These plates are usually hexagonal or pentagonal in the center and more rectangular around the edges. They fit tightly together to form the protective shell. In this sketch, I’m referencing the scutes of a box turtle. I draw the overall pattern first, then add texture by sketching ridges and growth rings on each plate.