Shark (Books)

Sharks are fish occasionally mentioned in the How to Train Your Dragon Book series.

Description
Sharks are a large group of fish belonging to the Superorder Selachimorpha. They are commonly known for their sleek shape, characteristic dorsal fin, and predatory nature. Physiologically, sharks are characterized by a skeleton made of cartilage rather than bone, five to seven gill slits, and pectoral fins not connected to their heads. Though there is a wide range of morphology and species, overall sharks have changed very little since their first appearance in the fossil record in the Ordovician period about 450 million years ago.

Similar to a cat, sharks have a tapetum lucidum in their eyes that reflects light in dark environments, increasing their sight in dark light conditions. Some species also have a nictitating membrane, or third eyelid, also similar to cats. Like many non-fish vertebrates, sharks can also dilate their pupils.

Function
In the Book series, sharks are mentioned as a descriptor for behavior and appearance.

In real life, sharks are eaten by humans, and used for their hides as well. They are also kept in public aquariums and zoos.

How to Train Your Dragon
Toothless is compared to a shark for his ruthlessness as a dragon.

"However, you only had to look into his big, innocent, heavily lashed eyes to realize that he was totally without morals. The eyes were ancient, the eyes of a killer. You might as well ask a crocodile or a shark to be your friend."

- Book 1