1. Scaleless sharks lived 380 million years ago and still retain some features of their ancestors. It has a fish-like head and seven fins, instead of five fins like most sharks. Its body is longer and has less muscles than the sharks we see today. Its most obvious uniqueness is that it has no scales, only a thin and fragile epidermis.
2. The spiny shark is a transitional species between sharks and bony fish. It is actually the first shark with a lower jaw. Just like a modern shark, its bones are made of cartilage, but its fins are supported by bone spurs like ordinary fish seen today. This shark is a filter-feeding animal with a cartilage rake in its mouth, which can catch food particles. It rarely grows more than 30 cm, but it is the largest filter-feeding animal that lived 400 million to 360 million years ago.
3. Eel Shark This is an ancient freshwater shark that died out 202 million years ago. This shark is only one meter long and looks more like an eel than a modern shark. Its back is covered with strip fins, and a sharp thorn sticks out from the back of its neck to provide protection. According to research, this kind of spine may be poisonous, similar to modern stingrays.
4. Broken sharks. This shark traveled all over the world from 1 100 million years ago to 85 million years ago, feeding on shellfish, and its powerful jaw can crush shells. These jaws are equipped with more than 550 flat teeth, which are very suitable for eating a lot of food needed by this 1 1 meter-long behemoth.
5. Sharks with sharp teeth. Toothed shark shared the ocean with marine dinosaurs from/kloc-0.00 to 75 million years ago, but it was still the ultimate predator. Plesiosaurs, Tyrannosaurus Rex, swordfish and even the biggest turtle are all on the shark's plate-even though they are all bigger than it. It is named after having 490 sharp teeth, each of which is 7 cm long and has an unusually thick enamel coating to keep the teeth sharp. It can grow to 7 meters and is the largest shark in existence.