Anomalocaris

This puzzling creature prowled through the oceans of our planet in the Cambrian period, over half a billion years ago; long before fish evolved to swim in them; longer still before animals even crawled out of the sea. It gets my vote because of two things:

1) It is weird enough in itself to be a sea-going version of the predator in the film Alien.

2) Its strangeness (and the fragmentary way in which most of its fossils are found) completely fooled paleontogists for more than half a century after it was first found; its grasping mouthparts were mistaken for shrimps (hence its name, which means “odd shrimp”); the mouth itself was described as a jellyfish (even though it bore a stronger resemblance to a pineapple slice than any species of jellyfish known) and its body (soft and hard to make out in its fossils) was classed as a sea cucumber.

In actual fact, it was the marine Tyrannosaurus of its time; by far the largest predator in those ancient long-vanished oceans.

I don’t know if it’s the only extinct animal to have its own homepage, but here is a link for those who would like to know a bit more about this strangest of killers.