Step 20: Use the angled line on the left, under the body, as a guide to draw the hind leg. Just like with the front legs, first lightly sketch the shape of the leg around the guide line. When you get the shape of the leg right, darken the lines. Add the small, V-shaped claws along the left edge of the turtle's foot.
Step 21: Draw the visible portion of the other hind leg under the middle section of the shell. Most of this leg will be hidden. Use the curved line on the right as a guide to draw the alligator snapping turtle's tail. Draw the shape of the tail around the guide. The base should be thick and the tip pointy.
Step 22: For a cleaner look, erase as much as you can of the initial guide lines. Don't worry about erasing all of the guides. The spikes can make that difficult to do. It's okay to leave some guides behind. Re-draw any final sketch lines you may have accidentally erased.
Final Step: Add some shading to your alligator snapping turtle drawing for extra detail. Use a dark value for the inside of the mouth. The lure on the tongue should be blank to emphasize it. The rest of the body should basically have a medium value. As you shade, add a few spikes on the skin using angled lines. Use a light value for the spikes to emphasize them. Use a dark value along the bottom of the body for shadows. Don't shade too smoothly. The rough value adds a bumpy, scaly texture.
Shading can be very time-consuming, so be patient and take breaks. As you shade the top part of the turtle's shell, use strokes that contour to the pyramid-like shape of each spike. Use a slightly darker value on one side of each spike to give them more dimension and volume. It's always a good idea to use reference when you draw. Don't forget to pause the video to draw to your own pace.
Add a cast shadow underneath. This helps ground the turtle so it doesn't appear to be floating.