Seadragonus Giganticus Maximus

The "preposterously huge" fire-breathing Sea Dragons are twenty time the size of the Big Blue Whale, and they are very dangerous -- they kill for fun. When two nasty Sea Dragons appear on the beach looking for a fight, Hiccup is the only one with a plan to save the tribe. They are frighteningly huge.

Anatomy
Sea Dragons are blue with an orange underside. They have heads that resemble a t-rex with narrow sharp teeth and the small frill of a triceratops. They have black spikes from the back of the neck to its tail, and wings with a single membrane. They also have gigantic legs with red spikes on them. It is the biggest dragon species ever seen, they can crush an whole viking village. It roars like a t-rex