what if scenario

If you could keep a prehistoric species as a aquarium pet, what kind would you want to keep and what size tank do you think it would require? I'm a big fan of Dunkleosteus, but with it being around the size of a great white shark it would need 5-10 million gallons of water. A smaller option...

If you were limited to keeping a single species of fish (Anthias, angelfish, clownfish etc.) which would it be and why? For me I would go with Gobies, you get a lot of different colors, body types, and size range for them so keeping multiple in a tank would be okay if done right.