Scientists get grip on Hallucigenia

Hallucigenia is a genus of Cambrian animals.

If Salvadore Dali were God, he would surely have designed an animal that looked like Hallucigenia.

It has been described as the most surreal creature that lived in the strangest period in the history of life on Earth, more than 500 million years ago.

After more than four decades of studying fossilised imprints, scientists believe they have finally nailed Hallucigenia's position in the tree of life, and in the process discovered its only living descendants.

Hallucigenia, named because of its dream-like, trip-inducing appearance, is one of the many marine animals that rather abruptly appear in the fossil record during a period in pre-history known as the Cambrian explosion, a biological bang that detonated the evolution of complex life-forms about 542 million years ago.

Until the Cambrian explosion, life had been bumbling along for about three billion years, with evolution producing nothing much more animate than a bath sponge. After the explosion, creatures with complex body plans evolved that walked, crawled, swam and burrowed. Hallucigenia was one of them.

Scientists were so thrown by Hallucigenia when its small fossils were first analysed 40 years ago that they thought its front end was its back end, and its top was its bottom.

They even thought it was an evolutionary one-off that had left no descendants alive today.

However, scientists now believe Hallucigenia is the ancestor of a small group of worm-like creatures with short, stubby legs that can be found today, living unobtrusively in the undergrowth of tropical forests.

Martin Smith and Javier Ortega-Hernandez of Cambridge University have detected key physical similarities between Hallucigenia and the so-called velvet worms, known more formally as the onychophorans - the first time zoologists have been able to rule conclusively on the creature's true role in history.

Their study, to be published in the journal Nature, is based on a detailed analysis of high-magnification images of the fossils of Hallucigenia.