Temporal range: Cambrian Stage 3–Middle Cambrian
|An artist's illustration of Hallucigenia fortis|
Conway Morris, 1977
Hallucigenia is an extinct genus of animal found fossilized in the Middle Cambrian-aged Burgess Shale formation of British Columbia, Canada, represented by the species H. sparsa, and in the Lower Cambrian Maotianshan shale of China, represented by the species H. fortis.
DiscoveryThe genus name was coined by Simon Conway Morris when he re-examined the various specimens of Charles Walcott's Burgess Shale worm genus Canadia in 1979. Conway Morris found that what Walcott had called one genus in fact included several quite different animals. One of them was so unusual that nothing about it made sense. Since the species wasn't a worm, Conway Morris had to come up with a new name to replace Canadia. He named the species Hallucigenia sparsa because of its "bizarre and dream-like quality" (like a hallucination). Hallucigenia was initially considered by Stephen Jay Gould to be unrelated to any living species, but most paleontologists now believe that the species was a relative of modern arthropods along with Anomalocaris and Opabinia. Other Lobopods from the Burgess Shale includes Anomalocaris, Opabinia, and Aysheaia. It's closely related to regular onychophorans and even Aysheaia. A another animal that also appeared in the Burgess Shale Burgessochaeta was even mistaken as a species of Canadia. When first discovered, it was often displayed upside-down.
Hallucigenia is unlike nearly any living animal today, although it was likely the ancestor to modern day arthropods. There were over 109 specimens of these strange aquatic creatures, and they ranged in size from 0.5 to 3 cm long. It had a round, worm-like body that was likely squishy to the touch.
Like arthropods and worms, it was an invertebrate, so it didn't have a backbone, however it did have hard, sharp spikes that stuck out of its back and likely kept potential predators away. It also had clawed, tentacle-like appendages that helped it move around the ocean floor. It had two tentacles out in front that were likely adapted to feeling its way around the bottom of the seas it lived in, and making sure it was going in the right direction, as Hallucigenia had only simple eyes on its face. Hallucigenia sparsa was likely a prey of Hurdia and Opabinia.
In 2015, the head of Hallucigenia was found showing it had a very different head than previously thought. What was originally thought to be the head was really just a stain of fluids that got out of the creature when it fossilized. The real head had a pair of simple eyes, and weirdly, what seemed to be a grin on its face.