Scientists Can Finally Tell This Bizarre Animal's Head From Its Tail

The fossilized remains of Hallucigenia sparsa were so strange, that paleontologists originally mistook its tail for its head. Now, four decades after its discovery, a Cambridge University research team has corrected this error with an updated reconstruction (and for an ancient sea worm that featured a frightening row of spikes, it was surprisingly cute).

The discovery of a Hallucigenia fossil featuring a pair of simple eyes and a ring of needle-like teeth allowed researchers Martin Smith and Jean-Bernard Caron to finally confirm which way the animal faced. The details of the new study can be found in the science journal Nature.


During the Cambrian Explosion some 500 million years ago, this 35mm long ecdysozoan was extremely common. Scientists now believe it’s distantly related to arthropods (insects and spiders), velvet worms, and tardigrades.

The researchers used an electron microscope to confirm that an orb-like structure at the animal’s rear end was a kind of excrement. As Smith told The Guardian, “The simple answer is poo. More technically, it’s a sort of soup of the inside of the animal that’s been squeezed out of the point of least resistance as it was squashed under layers of mud.”


Read more at The Guardian.

Contact the author at and @dvorsky. Top image: M. R. Smith & J-B Caron/Nature/YouTube; fossil image: M. R. Smith & J-B Caron/Nature; colorized reconstruction by Danielle Dufault/Nature

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