Smallpox and bubonic plague it is, then! Though they're not really animals, nor are they truly extinct.
This. Imagine the type/size of the cage you would need to dive with one of these animals. Being in the water with a creature that big and deadly would be rush unlike no other!
Or rule, if you look at it from a perspective of "what species can ruin what other species". It's a pretty hollow achievement, though. Especially when you think we've never really set out to make something extinct, but accomplished it through greed and short-sightedness.
