One of the most bizarre-looking fossils ever found - a worm-like creature with legs, spikes and a head difficult to distinguish from its tail - has found its place in the evolutionary Tree of Life, definitively linking it with a group of modern animals for the first time. 
 
 The animal, known as Hallucigenia due to its otherworldly appearance, had been considered an 'evolutionary misfit' as it was not clear how it related to modern animal groups. Researchers from the University of Cambridge have discovered an important link with modern velvet worms, also known as onychophorans, a relatively small group of worm-like animals that live in tropical forests. The results are published in the advance online edition of the journal Nature. 
 
 The affinity of Hallucigenia and other contemporary 'legged worms', collectively known as lobopodians, has been very controversial, as a lack of clear characteristics linking them to each other or to modern animals has made it difficult to determine their evolutionary home. 
 
 What is more, early interpretations of Hallucigenia, which was first identified in the 1970s, placed it both backwards and upside-down. The spines along the creature's back were originally thought to be legs, its legs were thought to be tentacles along its back, and its head was mistaken for its tail. 
 
 Hallucigenia lived approximately 505 million years ago during the Cambrian Explosion, a period of rapid evolution when most major animal groups first appear in the fossil record. These particular fossils come from the Burgess Shale in Canada's Rocky Mountains, one of the richest Cambrian fossil deposits in the world. 
 
 Looking like something from science fiction, Hallucigenia had a row of rigid spines along its back, and seven or eight pairs of legs ending in claws. The animals were between five and 35 millimetres in length, and lived on the floor of the Cambrian oceans. 
 
 A new study of the creature's claws revealed an organisation very close to those of modern velvet worms, where layers of cuticle (a hard substance similar to fingernails) are stacked one inside the other, like Russian nesting dolls. The same nesting structure can also be seen in the jaws of velvet worms, which are no more than legs modified for chewing. 
 
 "It's often thought that modern animal groups arose fully formed during the Cambrian Explosion," said Dr Martin Smith of the University's Department of Earth Sciences, the paper's lead author. "But evolution is a gradual process: today's complex anatomies emerged step by step, one feature at a time. By deciphering 'in-between' fossils like Hallucigenia, we can determine how different animal groups built up their modern body plans." 
 
 While Hallucigenia had been suspected to be an ancestor of velvet worms, definitive characteristics linking them together had been hard to come by, and their claws had never been studied in detail. Through analysing both the prehistoric and living creatures, the researchers found that claws were the connection joining them together. Cambrian fossils continue to produce new information on origins of complex animals, and the use of high-end imaging techniques and data on living organisms further allows researchers to untangle the enigmatic evolution of earliest creatures. 
 
 "An exciting outcome of this study is that it turns our current understanding of the evolutionary tree of arthropods - the group including spiders, insects and crustaceans - upside down," said Dr Javier Ortega-Hernandez, the paper's co-author. "Most gene-based studies suggest that arthropods and velvet worms are closely related to each other; however, our results indicate that arthropods are actually closer to water bears, or tardigrades, a group of hardy microscopic animals best known for being able to survive the vacuum of space and sub-zero temperatures - leaving velvet worms as distant cousins." 
 
 "The peculiar claws of Hallucigenia are a smoking gun that solve a long and heated debate in evolutionary biology, and may even help to decipher other problematic Cambrian critters," said Dr Smith. 
 
 ### ||||| 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 – and 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 they have finally been able to locate Hallucigenia’s position in evolutionary history by showing that it 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. 
 
 Fossil discoveries 
 
 
 
 
 
 
 
 6 show all Fossil discoveries 
 
 
 
 
 
 
 
 
 
 1/6 Archaeopteryx 1861: A hugely important fossil, this 147-million-year-old rock slab contains the remains of the earliest known bird. With its combination of bird and dinosaur characteristics, it is a famous snapshot of evolution in action. It's early discovery has since been queried as more complete examples were found (as above). 
 
 2/6 Ida - The Link 1983: Ida - a tiny 47-million-year-old fossil - was discovered at the Messel Pit southeast of Frankfurt am Main in Germany. But it was only in May 2009 that she was introduced to the world, at the head of a whirlwind publicity campaign as the supposed "missing link" in human evolution. Getty Images 
 
 3/6 Australopithecus sediba 2010: A partial cranium which belonged to human ancestor Australopithecus sediba, which was unearthed from a pit in South Africa AFP/ GETTY IMAGES 
 
 4/6 Darwinopterus 2010: The discovery of the fossil of the Darwinopterus filled a 155 million-year evolutionary gap PA 
 
 5/6 Fossil fight 2013: 'Astounding' fossil find from Montana revealing two dinosaurs locked in mortal combat 
 
 6/6 Ichthyosaur graveyard 2014: One of the 46 fossils found at the site in southern Chile Wolfgang Stinnesbeck 
 
 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, which grew no bigger than about 3.5cm long, showing five key characteristics that link the species to the velvet worms. 
 
 Video: Living fossils found surviving in China 
 
 Among the most important features is the way the claws at the end of its limbs are arranged. Under an electron microscope, each claw has two or three successive layers of cuticle nestled one within the other, like the layered skins of an onion. 
 
 Dr Smith said: “We think this enabled them to grow a new set of claws before they shed their skins, which they had to do to grow. A very similar feature is found in the claws and jaws of the velvet worms, and no other animal shares this particular characteristic. 
 
 “It means that the animals do not have to wait for a new claw to form after shedding their skin to grow – they already have one ready formed,” he explained. 
 
 Zoologists have also not always been completely sure which end of Hallucigenia is the front and which is the back, although Dr Smith said his research clears this up – the front has two or three pairs of appendages and the back has a rounded end where its body-length gut probably terminates. 
 
 It is now clear that the fearsome spikes on Hallucigenia’s back, which were once confused for stilt-like legs, are almost certainly a defensive mechanism against the increasing number of predators that emerged during the Cambrian explosion. 
 
 Fossils: Burgess Shale 
 
 The Cambrian explosion is named after the geological period that began about 541 million years ago, when a remarkable variety of marine animals first appear in the fossil record. 
 
 Most fossils are formed from the hard parts of living organism, such as bones or shells. However, details of the soft body parts of Cambrian creatures can be seen in a rock formation known as the Burgess Shale in the Canadian Rocky Mountains. 
 
 Hallucigenia was just one of many bizarre animals to live at this time. Other creatures included a fearsome predator called Anomalocaris, armed with two vicious-looking jaws and large eyes, and Wiwaxia, which looked like a Viking helmet with spikes. 
 
 For evolutionists, this period is one of the most interesting in the 3.5-billion-year history of life on earth because this was when many of the complex body plans seen in today’s animals are first detectable, even though they must have evolved from something earlier in history. 
 
 “It’s often thought that modern animal groups arose fully formed during the Cambrian explosion. But evolution is a gradual process,” said Martin Smith of Cambridge. 
 
 “Today’s complex anatomies emerged step by step, one feature at a time. By deciphering ‘in-between’ fossils like Hallucigenia, we can determine how different animal groups built up their modern body plans,” he said. ||||| 
 
 This is a reconstruction of the Burgess Shale animal Hallucigenia sparsa. (Elyssa Rider) 
 
 What has 20 legs, 14 sharp spikes on its back and a head that's really hard to distinguish from its rear end? Scientists didn't know either -- until recently. 
 
 It's called Hallucigenia because researchers have scratched their heads over where it fits among life forms since its fossil was discovered in the Burgess Shale of Canada's Rocky Mountains in the early 1970s. Unable to determine any living thing that evolved from it, they called it an "evolutionary misfit" for decades. 
 
 But a closer look into microscopes by scientists at the University of Cambridge finally yielded some clues that. A new study of the claws at the end of all those legs "revealed an organization very close to those of modern velvet worms," it says. 
 
 Like technicians who manicure fingernails and toenails, the researchers zeroed in on the animal's cuticles, which were stacked one inside the other, like those wooden Russian nesting dolls that open up only to reveal another doll. It was an oddity observed in at least one other place, the weird jaws of velvet worms, which, in the university's synopsis of the report, "are no more than legs modified for chewing." 
 
 That's right, legs that eat. 
 
 That stranger-than-science fiction reality finally solved a nearly 40-year-old puzzle. Hallucigenia, aptly named because people might have thought a person describing it was hallucinating, lived about 500 million years ago during the Cambrian Explosion, a period when most major animal groups first started to appear in the fossil record. 
 
 "It's often thought that modern animal groups arose fully formed during the Cambrian Explosion," Martin Smith, a professor at the university's Department of Earth Sciences and the study's lead author, said in a statement. "But evolution is a gradual process: today's complex anatomies emerged step by step, one feature at a time." 
 
 Smith and his co-authors painstakingly tracked strange fossils that appeared to evolve from the original. By "deciphering 'in-between' fossils like Hallucigenia," he said, they were able to determine how different animal groups built the bodies they inhabit today. 
 
 Here's what they looked like and where they lived, according to the study: "Hallucigenia had a row of rigid spines along its back, and seven or eight pairs of legs ending in claws. The animals were between five and 35 millimeters in length, and lived on the floor of the Cambrian oceans." 
 
 Because velvet worms are so weird, Hallucigenia was suspected to be an ancestor. But characteristics linking the two were not easy to find in the fossil record, and the details of the claws -- cuticles and such -- had not been closely reviewed. 
 
 Squinting hard and analyzing both the prehistoric and living animals, the claws were identified as a smoking gun joining the two. 
 
 The finding is a big deal, said Javier Ortega-Hernandez, a co-author of the study, because it turns what is known about the evolutionary tree of arthropods -- spiders, crustaceans and insects -- on its head. 
 
 "Most gene-based studies suggest that arthropods and velvet worms are closely related," Ortega-Hernandez said. But "our results indicate that arthropods are actually closer to water bears," he said. 
 
 He's not talking about an actual bear. Ortega-Hernandez was referring to a microscopic tardigrade, a little beast whose image can make a viewer's skin crawl, a thing with a round mouth full of teeth for attaching and sucking, with claws at the end of stubby legs. 
 
 Ortega-Hernandez spoke of tardigrades more fondly, calling them "a group of hardy microscopic animals best known for being able to survive the vacuum of space and sub-zero temperatures – leaving velvet worms as distant cousins."
– After four decades of confusion, scientists have finally figured out how to classify a creature so surreal it was given the name Hallucigenia. The tiny creature, found in fossils from the "Cambrian Explosion" of diverse life 500 million years ago, has 14 to 16 legs and large spikes on its back, and researchers have long puzzled over which end of it is meant to be in front. But after taking a close look at its claws, scientists have concluded that it isn't an evolutionary one-off as was once thought, but a relative of the tiny "velvet worms" with stubby legs that can still be found in tropical forests today, the Independent reports. Researchers say that the claws have much in common with the jaws of the velvet worms, which "are no more than legs modified for chewing," the Washington Post reports. The connection is exciting, researchers say, because it upends the previous understanding of the family tree of insects and other arthropods. "It's often thought that modern animal groups arose fully formed during the Cambrian Explosion," the lead researcher says in a press release. "But evolution is a gradual process: Today's complex anatomies emerged step by step, one feature at a time. By deciphering 'in-between' fossils like Hallucigenia, we can determine how different animal groups built up their modern body plans." (A crazy recent fossil find: penguins the size of NBA players.)