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Information about Hallucigenia and other prehistoric creatures.

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In 1977, British palaeontologist Simon Conway-Morris discovered the fossil of a truly weird animal, which he named Hallucigenia because of its "bizarre and dream-like quality". He wasn't kidding. The creature was so strange that it took fourteen years for scientists to work out which way up it stood. And now, nearly four decades after its original discovery, we finally know-clearly and conclusively-which end is the head.

Hallucigenia lived around 508 million years ago, and it was first unearthed in a famous Canadian fossil field called the Burgess Shale. When Conway-Morris set his eyes upon it, he saw a long tubular body, between 1 and 5 centimetres long. Seven pairs of long spines stuck out in one direction, while seven pairs of tentacles stuck out in the other, with what looked like little mouths on their tips. There was nothing distinct at one end, and a non-descript blob ballooning from the other. Where was the head? Or the back?

Conway-Morris guessed that the creature used its spines like stilts for walking along the ocean floor, while the tentacles plucked food out of the overlying water. Then, in 1991, a set of related Chinese fossils showed that Conway-Morris' reconstruction was upside-down. The "tentacles" were legs. The "mouths" on their tips were claws. And the "stilts" were spines that stuck out of the creature's back, probably for defence.

When I wrote about Hallucigenia last year, I said, "Even now, no one's entirely sure about the head." Some thought that the blobby balloon was rather head-like, but others said that it represented bodily fluids, which had leaked out the animal's backside after its death.

Now Martin Smith and Jean-Bernard Caron have finally solved that mystery. They looked at new well-preserved specimens, and also re-analysed the existing ones with the latest microscopes. "It was about time we took some modern techniques to see what secrets it had," says Smith.

Their analysis revealed that the head is the end opposite the blobby balloon. For a start, it has eyes. They appear as a pair of dark spots, which "really pop out under an electron microscope," says Smith. These spots probably represent the visual pigments that were part of the animal's original eyes. Since they appear as solid masses rather than spotty grids, they imply that Hallucigenia had simple eyes rather than the compound ones of insects.

The end with the eyes also had a mouth-again, clearly the head. There was a hole with a ring of spines around it, and further back, a set of needle-like teeth in the throat. That sounds like a fearsome set-up but there's nothing predatory about Hallucigenia. Instead, Smith thinks that it used the spines to make its mouth rigid so it could suck up its food, while the throat teeth helped to ratchet its mouthfuls towards its stomach. (In some specimens, Smith and Caron could even make our the creature's entire gut.)

Behind the head, Hallucigenia had 10 pairs of limbs. The first three were slender, short, and clawless. Who knows what they were for? They could have been sensory organs, like antennae. They might have been covered in feathery growths for filtering plankton from the water. They might even have acted as tentacles. "You can imagine them cuddling a sponge," says Smith.

The last seven pairs of limbs are clearly legs, though, and "in many specimens, it was clear that the body ends with a pair of legs," says Smith. The legs had no joints, so Hallucigenia probably controlled them by changing the pressure of the fluid within, much like starfish and sea urchins do today. Alternatively, the large spines on the back might have acted as anchor points for large muscles, which powered into the legs. After all, there were seven pairs of spines and seven pairs of legs. Perhaps this extinct weirdo was a walking suspension bridge.

These discoveries are relevant to more than just Hallucigenia. The animal was most closely related today's velvet worms-glue-spitting, colourful, multi-legged creatures. That would make them part of the ecdysozoans-a super-successful group of animals that includes insects, spiders and scorpions, crustaceans, centipedes and millipedes, nematode worms, velvet worms, and lesser known groups like the invincible tardigrades and the unfortunately named penis worms.

The mouths of these creatures are extremely variable. The velvet worms and arthropods basically have simple holes with unarmed throats. The penis worms, however, have mouths that are surrounded by spines and throats that are covered with teeth-which are uncannily close to what Smith and Caron saw in Hallucigenia. This suggests that the ancestor of the ecdysozoans also had similarly complex mouthparts, which were then lost in some lineages like the velvet worms.

Hallucigenia might have more to say about the ancestry of this super-group, but for now, Smith is content about finally knowing what it looks like. "I think it's pretty unambiguous what we're looking at," he says. "I don't think we're going to turn it over again or back to front."

Reference: Smith & Caron. 2015. Hallucigenia's head and the pharyngeal armature of early ecdysozoans. Nature http://dx.doi.org/10.1038/nature14573

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Scientists Finally Decide Which Bit of This Weird Animal is the Head

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In 1977, British palaeontologist Simon Conway-Morris discovered the fossil of a truly weird animal, which he named Hallucigenia because of its "bizarre and dream-like quality". He wasn't kidding. The creature was so strange that it took fourteen years for scientists to work out which way up it stood.

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My daily moment of extreme nerdiness: Of Hallucigenia, velvet worms and water bears

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I am experiencing sheer, pure nerdiness, and I am loving every minute of it. Before I get into topic, I want to categorically state that I am a proud nerd. Why? Some of my thoughts are explained here. Ok, what triggered these feelings today? I heard about this paper: Hallucigenia's onychophoran-like claws and the case for...

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A weird and wonderful history

In 1977, British paleontologist Simon Conway-Morris came across a very weird-looking fossil. It had been found in the Burgess Shale, in the Canadian Rockies, 66 years prior. And the people who found the 0.5-inch long fossil had classified it as an annelid worm - worms that include leeches and earthworms. But when Conway-Morris took a look at it, he begged to differ. As far as he was concerned, this organism had walked on seven pairs of stilt-like spines, all while waving around the seven wacky tentacles on its back. Conway called it Hallucigenia - since it seemed like something a person might dream up during a trip gone wrong

Long gone are the days of butt-heads and spine-feet Ramskold, 1992

Conway-Morris' model was controversial, but it stood until 1991. That year, researchers Lars Ramskold and Hou Xianguang discovered fossils in China belonging to a related animal called Microdictyon - fossils that made Conway-Morris' mistake quite clear. These animals sported plates instead of spines on their back, which made it easy to identify their "tentacles" for what they truly were: legs. Conway-Morris had been looking at Hallucigenia upside-down the whole time. So, the scientists flipped it.

One mystery remained, however. Which end housed Hallucigenia's head? Conway-Morris figured it was the blob-like structure located at one end of the Burgess Shale fossil. But in 1992, Ramskold suggested that the blob might just be a stain that was made when Hallucigenia died; the stain was created when "decay fluids" seeped out of the animal upon its death. Beyond this suggestion, however, it was hard to definitely tell which end of the animal was which - until now, that is.
Hallucigenia sparsa from the Burgess Shale. Credit: Jean-Bernard Caron
A model for all time

"When we put it in the electron microscope, we saw not just the pair of eyes, but also this big smile of teeth grinning back at us - and that really resolved for all of us not just the position of the head, but all of the detail in that as well," explains Martin Smith, a paleontologist at the University of Cambridge and a co-author of the new Hallucigenia study, published in Nature today.

Based on their analyses, Hallucigenia not only sported long spines on its back - spines that were probably used for defense, Smith says - but teeth around its mouth, a pair of simple eyes, and teeth inside the throat-like area of its gut, to aid in digestion. The scientists now also have a much better idea of how its limbs and spines were constructed.
"Not just the pair of eyes, but also this big smile of teeth grinning back at us."
Because of these newly identified features, it's now possible to imagine how Hallucigenia interacted with the aquatic world surrounding it, 508 million years ago. "It wouldn't have had clear vision," Smith says. Hallucigenia lived deep underwater, where light is scarce. It was probably about to make out organisms swimming overheard, and their shadows. "It would have been able to tell day from night," Smith says.

Scientists don't know what Hallucigenia ate, but the mouthparts hint at a kind of suction mechanism. "The ring of teeth around the mouth were probably involved in sucking water and food into the gut," Smith says, adding that the teeth inside the "throat" area would have kept the food from moving backwards. "It just sucked whatever it could; it wasn't chewing stuff."

As for its floppy legs, it's entirely possible that they were too flimsy to really help Hallucigenia "walk," Smith says. "You can imagine him hugging or clinging onto a sponge or a seaweed or something like that, and climbing up the sponge and feeding on that."

While it clung to sponges, its spines provided some protection. "There were probably some quite nasty predators swimming around," Smith says. Scientists have discovered fossils of predators such as squids and "lobsters crossed with can openers" that were "really sort of bizarre and quite fearsome," Smith says. Predators that went after Hallucigenia may have received a nice stabbing in return.

"You can imagine him hugging or clinging onto a sponge."

Hallucigenia wears its name well; it's a floppy hallucination and a complete blast from the past. But the physical features described in Nature today represent a lot more for biologists than you might expect. They can be used to clear up some pretty big questions regarding the evolution of "Ecdysozoa" - "one of the most large and diverse animal groups on the planet," Smith says.

Prior to this discovery, similar genes and the ability to molt were the only features that united animals like hookworms, tartigrades, and spiders. Now, it looks like the plates around Hallucigenia's mouth - teeth that are featured in some worms - and the teeth lining its gut, which appear in some crustaceans, can also be used to link the three. "What Hallucigenia has shown us is a physical, anatomical feature that unites this entire group," Smith says. Certain subgroups simply lost these features as time went on.

"This major discovery is what makes it a really significant paper," says Peter van Roy, a paleontologist at Yale University who didn't take part in the Hallucigenia study. "It shows that these circular oral plates is a character of Ecdysozoa, in general." In short, they didn't pop up independently. These features would have been present in the last common ancestor, as well.

Better technology, better models

Advances in microscope technology made this new model possible, Smith explains. To reach this model, Smith and his colleague, Jean-Bernard Caron, observed more than 100 Hallucigenia fossils unearthed in national parks, using electron microscopes. Electron microscopes use beams of electrons to illuminate a specimen. A few years ago, using one would have meant spraying irreplaceable fossils with gold particles that can conduct electrons, Smith says. "That wouldn't have gone down particularly well." Today, paleontologists can use a very fine mist of water instead. "You don't have to damage fossils at all," Smith says.

But if advances in technology are the main reasons this model was created, what's stopping even better microscopy techniques - or better fossils, for that matter - from coming along and turning this into yet another butt-to-face fiasco?
"I'm pretty confident that this is what the animal looked like."
"Our knowledge will always improve, and no doubt there will be small adjustments, but I'm pretty confident that this is what the animal looked like," Van Roy says. The researcher has access to a lot more data than previous groups did, and "our knowledge has been developing since the 1990s," he says. Hallucigenia, in its current form, "makes sense."

"In terms of its actual biology, we still know a lot less about them than we would if it were alive today," Smith concedes. But overall, "we've got a pretty good understanding there - I don't think this is something where we are going to find out that the head is the tail."

Scientists rarely get everything right the first time around. Fortunately, science is self-correcting. It may have taken half a century, but researchers might have finally gotten this weirdo right. Surely, we can bask in the glory of its strangeness for a spell.

"We've known this animal for over 100 years, and it just sort of seems wrong that we didn't know which end was the head and which end was the tail," Smith says. "Even just finding out where the head was was quite exciting, so the fact that it's also key to unlocking a recognized, but poorly defined group... that was really the icing on the cake, I suppose."

Verge Video: Can we bring animals back from extinction?

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After 50 years, scientists discover head of the insane Hallucigenia 'worm'

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In 1977, British paleontologist Simon Conway-Morris came across a very weird-looking fossil. It had been found in the Burgess Shale, in the Canadian Rockies, 66 years prior. And the people who found the 0.5-inch long fossil had classified it as an annelid worm - worms that include leeches and earthworms. But when Conway-Morris took a look at it, he begged to differ.

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Un grupo de fósiles permite reconstruir el aspecto de la criatura

Fue hallado en Canadá y data de hace 500 millones de años

Este peculiar aspecto ha generado gran confusión entre los científicos. Cuando se identificaron los primeros restos en los años 70, la reconstrucción de la Hallucigenia fue completamente a la inversa, es decir, los expertos pensaron que las espinas eran tentáculos, al igual que las piernas, y que la cabeza era la cola.

El análisis de casi 100 fósiles encontrados en la ladera de una montaña del Parque Nacional de Yoho, en las Montañas Rocosas de Canadá, permitió a Smith y su equipo resolver las dudas que todavía quedaban sobre dónde se situaba la cabeza.

Lo que se pensaba que podía ser la cola, en realidad no formaba parte del cuerpo del animal

"Esta dentadura supone una morfología compleja para una especie tan antigua. Esperábamos hallar una anatomía más primitiva", manifiesta el científico.

"Por tanto, podemos confirmar morfólogicamente que todas las especies que cambian de piel -los panartrópodos y los cycloneuralia- comparten un ancestro común, algo que hasta ahora solo se había podido determinar a través del análisis molecular del ADN", concluye el investigador.

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Fundaciondinosaurioscyl Salas de los Infantes

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Un gusano con espinas y dientes, antecesor de buena parte de los actuales invertebrados

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Un grupo de fósiles permite reconstruir el aspecto de la criatura Fue hallado en Canadá y data de hace 500 millones de años Este peculiar aspecto ha generado gran confusión entre los científicos.

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Hallucigenia's head and the pharyngeal armature of early ecdysozoans. 2015. Nature

Abstract: The molecularly defined clade Ecdysozoa comprises the panarthropods (Euarthropoda, Onychophora and Tardigrada) and the cycloneuralian worms (Nematoda, Nematomorpha, Priapulida, Loricifera and Kinorhyncha). These disparate phyla are united by their means of moulting, but otherwise share few morphological characters-none of which has a meaningful fossilization potential. As such, the early evolutionary history of the group as a whole is largely uncharted.

Here we redescribe the 508-million-year-old stem-group onychophoran Hallucigenia sparsa from the mid-Cambrian Burgess Shale. We document an elongate head with a pair of simple eyes, a terminal buccal chamber containing a radial array of sclerotized elements, and a differentiated foregut that is lined with acicular teeth. The radial elements and pharyngeal teeth resemble the sclerotized circumoral elements and pharyngeal teeth expressed in tardigrades, stem-group euarthropods and cycloneuralian worms.

Phylogenetic results indicate that equivalent structures characterized the ancestral panarthropod and, seemingly, the ancestral ecdysozoan, demonstrating the deep homology of panarthropod and cycloneuralian mouthparts, and providing an anatomical synapomorphy for the ecdysozoan supergroup.

The topology shown denotes a newly retrieved 'hallucishaniid' clade-diagnosed by a swollen head, dorsal spines, and the differentiation of the anterior trunk and trunk appendages-includes luolishaniids, Orstenotubulus (not shown) and Carbotubulus within a paraphyletic 'Hallucigenia'.

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Hallucigenia's head and the pharyngeal armature of early ecdysozoans. 2015. Nature Abstract: The molecularly defined clade Ecdysozoa comprises the panarthropods (Euarthropoda, Onychophora and Tardigrada) and the cycloneuralian worms (Nematoda, Nematomorpha, Priapulida, Loricifera and Kinorhyncha). These disparate phyla are united by their means of moulting, but otherwise share few morphological characters-none of which has a meaningful fossilization potential.

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Head or tail? Elyssa Rider, Author provided

A bizarre 500-million-year-old "worm with legs" has finally found its rightful place on the evolutionary tree of life. Fossils of Hallucigenia look so odd that scientists couldn't make head or tail of it, quite literally. With its alien-looking legs and intimidating spines, it was thought to represent a long-extinct body form. But, for the first time, a new study we published today in Nature links Hallucigenia to a modern group of animals - the rainforest-dwelling velvet worms.

A palaeontological puzzle

Martin Smith/Smithsonian Institute

Hallucigenia has posed a challenge for palaeontologists. It is difficult to classify because it shares few features with modern animals. When it was first described in the 1970s, the spines along its back were mistaken for legs, and even today scientists have yet to agree which end is its head and which is its tail.

Vexed by this mystery, I used state-of-the-art electron microscopes to examine centimetre-long Hallucigenia fossils from the Burgess Shale in Yoho National Park, Canada. The movement of the Earth's crust thrust this treasure trove of fossils to the top of the Canadian Rockies, but it was laid down on a sea floor long before even the simplest plants had emerged onto land.

When magnified 1,000 times, the fossils revealed that Hallucigenia's claws had multiple layers, stacked one inside the other like a conical onion. This prompted me to take a closer look at modern velvet worms, to which Hallucigenia had been tentatively linked.

Martin Smith

Careful microscopy showed that that these worms have the same onion-like layers in their claws. And each time the animals moult, the outer sheath falls away to expose a fresh layer beneath.

To test whether this connection denoted a biological relationship, I enlisted the help of my colleague Javier Ortega-Hernández. Together, we scoured the scientific literature for fossil worms from the same group as Hallucigenia - the lobopodians. We then searched for family trees that were consistent with our data on living and fossil creatures.

Our optimal tree shows that velvet worms are indeed distant relatives of Hallucigenia, separated by half a billion years of evolution. But other lobopodians belong elsewhere. Some fall among the ancestors of arthropods, the group that includes millipedes, insects, spiders and crabs. Others are related to tiny moss-dwelling animals called tardigrades or water bears.

From dead end to lay-by

It is often thought that modern animal groups, such as arthropods, arose fully formed in a sudden burst of biodiversity called the Cambrian Explosion, about 540 million years ago. But Hallucigenia 's new position on the tree of life closes the gaps between these modern groups, and shows that Cambrian evolution proceeded in small increments rather than great leaps.

Modern velvet worms are tropical predators adapted to life among logs and leaf litter. They have glands to squirt sticky slime at insect prey, have modified their forelimbs into fearsome jaws, and are covered with tiny whiskers that feel their way through cracks in logs.

Andras Kezzei/Flikr

Hallucigenia did not have such glands, jaws or whiskers, which would after all be of little use under the sea. But because it did have onion-layer claws, Hallucigenia was not an evolutionary dead end. Rather, it represents an early pit stop on the way to the velvet worm body plan, which arose gradually over time.

Other lobopodians turn out to have equivalent relationships to arthropods and water bears, showing some but not all of the features that define these modern groups. So we no longer need to view Hallucigenia and other lobopodians as evolutionary oddballs. Rather, they represent deep branches in the tree of life, and provide a unique insight into the origins of modern animal diversity. After all, without the fossils, who would have guessed that the cuddly velvet worms evolved from an ancestor as ghoulish as Hallucigenia?

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The world's weirdest creature finds descendants in cuddly velvet worms

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A bizarre 500-million-year-old "worm with legs" has finally found its rightful place on the evolutionary tree of life. Fossils of Hallucigenia look so odd that scientists couldn't make head or tail of it, quite literally. With its alien-looking legs and intimidating spines, it was thought to represent a long-extinct body form.

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Based on the appearance of those initial fossil preparations, the first restoration made in 1977 presented us with an animal walking along the bottom of the seafloor on spiny stilts, waving seven dorsal tentacles from its back. The "tentacles" seemed to have a mouth at each tip.