As It Happens

Researchers unravel bizarre prehistoric sea creature fossil

It looks like something surrealist H.R. Giger might have dreamed up, but the prehistoric sea creature Hallucigenia may hold the key to understanding how organisms developed hundreds of millions of years ago.
Hallucigenia was a prehistoric worm-like sea creature that lived 500 million years ago. (Illustration by Danielle Dufault, photo by Jean-Bernard Caron, Royal Ontario Museum)

It looks like something surrealist H.R. Giger might have dreamed up ... a prehistoric, worm-like sea creature covered in spikes and spiked tentacles. 

Scientists call it Hallucigenia, and for decades they knew very little about the pre-historic sea creature that lived more than 500 million years ago. Researchers couldn't tell which end of its worm-like body was its head, or even if it had one. Until now. Studying new fossils discovered in the Rocky Mountains, a British-Canadian research team has given us the first detailed descriptions of what Hallucigenia looked like. 

It turns out scientists' original understanding of the tiny organism, which was the width of a pin and only a centimetre or two in length, was upside-down and backward. In the 1970s, it was thought its back spikes were legs, and its legs were tentacles along its back. And its head was its tail.

"Even when we had the animal the right way up, it still wasn't clear which end was the head and which was the tail," explains Martin Smith, a postdoctoral researcher in Earth Sciences at the University of Cambridge, who led the team.

"When we put it in [the microscope] we were sort of hoping we would see eyes or something that would confirm it was the head. We saw a pair of eyes looking back at us. But much more surprisingly, underneath the eyes was a really cheeky little smile. It was like it was teasing us for taking so long to find the head."

The "smile" was created by needle-like rows of inverted teeth that lined the throat of the animal, pointing backward toward the stomach. Smith speculates that the teeth were used to help suck food into the organism, and prevent it from escaping out again. 

Finding the teeth was unexpected, as they hadn't been seen before along the organism's evolutionary chain. Now, Smith says the discovery has redrawn the organism's evolutionary tree. 

Hallucigenia is one of the species emblematic of the Cambrian Period, a pivotal juncture in the history of life on Earth when most major groups of animals first appeared and many unusual body designs came and went.

Hallucigenia, whose fossils have been unearthed in the Burgess Shale site in the Canadian Rocky Mountains, belongs to a primitive group of velvet worms, animals that still exist today. It had seven pairs of nail-like spines protruding from its back, with an equal number of pairs of long, flimsy legs underneath, tipped with claws. There were three pairs of skinny tentacles toward the head, perhaps used to process food or as antennae. 

Smith says he's hopeful that newer fossils found in the Canadian Rockies will contain nerve tissue, which would unlock even more secrets from this strange prehistoric organism. 

The research appears in the journal Nature.

- With files from Thomson Reuters


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