21. Stethacanthus
The Stethacanthus beast was a very real shark species that lived within our oceans hundreds around 320 million years ago. That makes this species among the first known shark species in existence. The way they looked differed from the multiple types we see today, however.
They had an anvil-shaped fin, which was used for attracting mates and intimidating other potential predators. They were relatively small compared to the larger animals around them. This is why scientists believe they were bottom feeders during their time. However, like sharks of today, they had sharp teeth and strong bodies. This allowed them to take down some bigger animals, especially when attacking in group form.