I've been working for a while on this. One of the main themes of my book is that every animal is associated with one or more of the elements and that dragons are the only creatures with all four. In the book, dragons are a type of drake; and drakes also include salamanders, amphiteres, leviathans, wurms, and variants thereof. Salamanders are associated with fire, amphiteres with air, leviathans with water, and wurms with earth. They're pictured in that order starting at the top and moving in a clockwise direction.