Step 6: To the left of the head, draw a small arc as a guide for the Diplodocus's muzzle.
Step 7: On the right side of the body, draw a very long line as a guide for the whip-like tail. Diplodocus had extremely long tails, so curve your line down if you don't have enough room to draw the entire thing on the right side. The tail, along with the dinosaur's body and neck, should have a long, horizontal orientation.
Step 8: Under the body, on the left side, draw a vertical line that slopes to the right and then bends to the left as a guide for the first front leg. To the left, draw a vertical line that slopes to the left and then bends to the left at the bottom for the Diplodocus's other front leg.
Step 9: Under the Diplodocus's body on the right side, draw a longer vertical line that bends near the middle and at the bottom as a guide for the first hind leg. To the right, draw the guide for the visible portion of the other hind leg as a shorter vertical line that bends at the bottom.
That's it for the guides! From this point on, press harder with your pencil for a more defined drawing.