Since its first fossils were found more than 100 years ago, Hallucigenia has perplexed paleontologists. Looking like a cross between a hockey stick and a pincushion, the 1cm to 5cm long creature was named to reflect its surreal and “dream-like” appearance. It was first described on its side, then upside down walking on its long spines, and finally inverted to walk on what we now believe were its legs. Even then, scientists have been unable to agree on which end of the animal is the head and which is the tail.
My colleague Jean-Bernard Caron and I became interested in Hallucigenia when we found that electron microscopes could reveal new details of its fossilized spines and claws. This helped us establish the creature’s place in the tree of life by working out its evolutionary relatives. Given the dozens of specimens collected by Royal Ontario Museum teams from the Burgess Shale in Yoho National Park, Canada, we thought we might finally have a chance to understand this oddball animal.
Prior to our study, a large balloon-shaped orb at one end of the specimen had been interpreted as an amorphous head. We soon established that this wasn’t part of the body at all but a dark stain representing decay fluids or gut contents that oozed out of the rear end of the animal as it was buried.
I first became aware of Hallucigenia while reading Gould’s wonderful book,Wonderful Life: The Burgess Shale and the Nature of History.
The book dealt with the bizarre forms of life seen around the Cambrian explosion, with the thesis that random chance events produced the phylums we see today and that if we rewound time that things would be very different.
At the time (1990), Hallucigenia was seen as a totally oddball creature with no modern descendents. It was like some alien form of life that existefor a period then disappeared.
Bu in the 30 years since, a lot of been clarified and while Hallucigenia is still quite odd, it does seem to now fit in the standard scheme of things instead of outside it.
I’d like to think that Gould would agree with the last paragraphof this article:
I’ve always loved Hallucigenia for being such an unusual and surprising beast. Each time we uncover one of its secrets it seems to make us think again about something we thought we knew. I only wonder what surprises Hallucigenia will reveal next.