Final answer:
The characteristics of Toothless' saddle and tail fin can be explained by the fact that Toothless is a member of the group Chondrichthyes, which includes sharks and rays. These animals have specific features like a backbone, jaws, and thin, bony fins. They also have a heterocercal caudal fin, where the fin lobes are unequal in size.
Step-by-step explanation:
Toothless' saddle and tail fin are examples of characteristics of a group of animals called Chondrichthyes, which includes sharks and rays. These animals have a backbone and jaws, an endoskeleton made of bones, and thin, bony fins. They also possess a heterocercal caudal fin or tail, which means the fin lobes are unequally sized, with the tail vertebrae extending into the larger upper lobe.