More than 100 years later, scientists can finally tell animal's head from its butt

A strange sea creature's embarrassment is over. More than a century after the now-extinct Hallucigenia was first found, scientists say they've discovered which end is its face and which is its butt.

In Hallucigenia's defense, all fossils of the tiny creature—which was thinner than a hair when it roamed the world 500 million years ago, notes the BBC—seemed to be missing a head, which made imagining the creature pretty difficult.

For the first time, though, scientists have found samples in Canada that show the entire creature intact, according to a Nature study. In addition to a body covered in spikes, 10 pairs of clawed limbs, and three pairs of tentacles, per Reuters, scientists can identify a spoon-shaped head, "a tiny pair of eyes looking back at us" and "beneath them a really cheeky semi-circular smile," says researcher Martin Smith.

"Surreal." Behind the smile sits two sets of teeth, a circle of teeth in the mouth, and needlelike teeth that run down its throat. Smith suggests Hallucigenia probably sucked up its food—possibly tiny particles in water or bits of sponge—"like a plunger," while the teeth helped move the food toward its stomach, reports LiveScience.

The ring of teeth could link Hallucigenia to ecdysozoans like spiders and worms, Smith says. Some ecdysozoans have similar "O"-shaped mouths with rings of teeth, but others, like spiders, don't.

Smith guesses an early ancestor probably had a toothy mouth that some descendants kept, while others evolved a simpler mouth. The new research also helps scientists explain an orblike spot in Hallucigenia fossils that was once thought to be its head.

Smith says it is instead "a blob of decay fluids that oozed out of the anus during decay and burial." (This ancient sea creature was the size of a motorboat.)

This article originally appeared on Newser: Scientists Can Finally Tell Animal's Head From Its Butt

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