"I popped off the feet and put fish flippers on this turtle ...let's do it to the elephant!" [sheldoncomics.com]

I hope this was an intentional hidden reference to manatees, because it's hilarious.

Manatees are thought to have evolved from four-legged land mammals some 60 million years ago; a common ancestry shared with elephants, their closest living relatives.

So, basically, yeah. That's how they made manatees.