A creature so weird, a scientist thought he was hallucinating
He, and scientists ever since, have not been able to make head nor tail of the animal – literally they didn't know which end was which.
Now, using electronic microscopes, Martin Smith at Cambridge University and his colleague Jean-Bernard Caron at the University of Toronto, have figured it out.
Their discovery was published in Nature.
Hallucigenia - a worm-like animal with legs and spikes along its back – lived 500 million years ago. It is the common ancestor of everything from tiny roundworms to lobsters.
The creature had a throat lined with needle-like teeth, a previously unidentified feature which could help connect the dots between it, modern velvet worms and arthropods.
Arthropods, velvet worms (onychophorans) and water bears (tardigrades) all belong to the massive group of animals that moult, known as ecdysozoans. Though Hallucigenia is not the common ancestor of all ecdysozoans, it is a precursor to velvet worms. Finding this mouth arrangement in Hallucigenia helped scientists determine that velvet worms originally had the same configuration - but it was eventually lost through evolution.
"The early evolutionary history of this huge group is pretty much uncharted," said Smith. "While we know that the animals in this group are united by the fact that they moult, we haven't been able to find many physical characteristics that unite them."
Hallucigenia was just one of the weird creatures that lived during the Cambrian Explosion, a period of rapid evolutionary development starting about half a billion years ago, when most major animal groups first emerge in the fossil record.
The video below shows how scientists believe Hallucigenia walked.