2 Indicate texture and detail
I begin to add in textures, ridges, damage and detail into the ornamentations. Some animals, like the iguana, have fleshy dewlaps so it requires a different approach to detail and texture, and reference becomes important. Go to zoos, museums, watch nature documentaries and search hi-res images. Nature is seldom perfect. Adding nicks, damage and uneven edges enhances the drawing.
Start light with your pencil and work up those textures. Remember to keep them sparse and random looking. Drawing chips to the horn and irregular textures can add personality to your animal.