Ancient Hallucigenia Creature Rears Its Head After 500 Mln Years

The mystery of the appearance of Hallucigenia, which lived 508 million years ago, has finally been laid to rest by a new fossil study which has reconstructed the animal and definitively identified its head for the first time.

"Prior to our study there was still some uncertainty as to which end of the animal represented the head, and which the tail," said Dr Martin Smith, a researcher at Cambridge University's Department of Earth Sciences, and the paper’s lead author. 

"A large balloon-like orb at one end of the specimen was originally thought to be the head, but we can now demonstrate that this actually wasn’t part of the body at all, but a dark stain representing decay fluids or gut contents that oozed out as the animal was flattened during burial."

Hallucigenia was identified by British paleontologist Simon Conway Morris in the 1970s, who gave it the name 'Hallucigenia sparsa' because of its strange appearance. Previous attempts at reconstructing the creature mistook its tail for its head, and the spines along its back were thought to be legs. 

In August last year year scientists published the results of a previous study of Hallucigenia, which analysed its claws and was able to finally place it in the 'Tree of Life,' as a precursor to modern velvet worms, part of the massive group of moulting animals, known as ecdysozoans and including arthropods and water bears. 

According to the research published on Wednesday in the journal Nature, the creature had an elongated head with simple eyes, and a throat lined with needle-like teeth. The discovery of its teeth has helped scientists to determine that velvet worms originally had the same configuration of teeth, but lost it through evolution.

"It turns out that the ancestors of moulting animals were much more anatomically advanced than we ever could have imagined: ring-like, plate-bearing worms with an armoured throat and a mouth surrounded by spines," said Dr Jean-Bernard Caron, a Professor of Earth Sciences at the University of Toronto. 

"We previously thought that neither velvet worms nor their ancestors had teeth. But Hallucigenia tells us that actually, velvet worm ancestors had them, and living forms just lost their teeth over time." 

Hallucigenia were between 5 and 35 mm in length and lived on the ocean floor during the Cambrian Explosion, a period of rapid evolution when most major animal groups first appear in the fossil record.