It Took Scientists Almost 40 Years to Figure Out What Part of This Animal Is the Head

Millions of years ago, very different creatures roamed the earth—some so foreign to the modern world that scientists can’t even figure out how they would have stood up, much less which part of them was the head. Such is the case with Hallucigenia, a kind of spiky, tubular worm-creature that lived some 508 million years ago. A new study in Nature reveals where exactly the ancient animal’s head would have been—and points out its eyes for the first time. 

The blob on the right of the image above is not a head, but decay fluids (Df). The head is on the left. Image Credit: Smith et. al, Nature (2015)

First discovered in the Burgess Shale fossil field in Canada in 1977, it took almost 15 years for scientists to figure out how the sea creature stood up. The scientist who unearthed the fossil of a long, tubular body with seven pairs of spines and seven pairs of tentacles initially thought it walked along the ocean floor on its spines (using them like stilts) and used the tentacles to grab food. In 1991, further research revealed that the initial hypothesis was upside down: the tentacles were legs, and the spikes were located on its back for defense. At the end of its legs were claws.

Watch this scientific illustration of Hallucigenia, and try not to laugh too hard imagining this thing walking toward you: 

But was the 

blobby appendage (the right side of the second fossil image above) located on one end of the body its head, or its butt? Admittedly, when looking at a flattened outline of the animal millions of years after its demise, it’s pretty hard to tell. Based on new analysis of specimens, Cambridge’s Martin Smith and Jean-Bernard Caron of the Royal Ontario Museum argue that the head is, in fact, at the opposite end from the blobby part, shown in fossil images, which was once thought to be the head. 

The head is on the left (b) in the image above. Image Credit: Smith et. al, Nature (2015)

Under an electron microscope, the researchers were able to identify a mouth and two clear dark spots that they hypothesize are remnants of the creature’s eyes. The mouth had a ring of spines around it to help it vacuum up food, and teeth in its throat to move the food into its gut. The legs had no joints, and it probably moved like a starfish, through pressurized fluid.

It looks like a cross between a dinosaur, a centipede, and a sea anemone.