It is the year 2020, as it is in any other generic post-apocalyptic scene. The earth is a large chunk of ice. The population of humans is dwindling, and so is every other animal. Except one.
The penguin. It's population is rising constantly. Exceeding humankind by far. They are able to survive in such condition, feasting off other creatures' flesh. Then when all other creatures are gone from existence, one remains.
The human. It searches, constantly hunting for one. It seeks a lone wanderer, crawling for food, and minutes later, he is devoured, all skin and bones, leaving no traces of his existence. Then it searches again, and again.
So the cycle goes, until one day. It stumbles upon an encampment of humans, the only humans remaining. The penguins, armed with teeth, which have been developed through slowly becoming carnivores, rush forward sliding through the ice. The humans stumble, one trips, and that is his mistake. Devoured. In a split second too.
The others retreat, but penguins march in from the other side, gnashing their teeth. They advance, cornering the humans. One human pulls out a rifle, and begins shooting. Few penguins die but one grips on to the rifle, and snaps it in two. Then they advance and devour the rest.
With nothing else to eat, they die out, until no life remains.