̽��ֱ�� of Cambridge - Javier Ortega-Hernandez

520 million-year-old fossilised nervous system is most detailed example yet found

sc604 — Mon, 29 Feb 2016 20:00:00 +0000

Researchers have found one of the oldest and most detailed fossils of the central nervous system yet identified, from a crustacean-like animal that lived more than 500 million years ago. ̽��ֱ��fossil, from southern China, has been so well preserved that individual nerves are visible, the first time this level of detail has been observed in a fossil of this age.

̽��ֱ��findings, published in the Proceedings of the National Academy of Sciences, are helping researchers understand how the nervous system of arthropods - creepy crawlies with jointed legs - evolved. Finding any fossilised soft tissue is rare, but this particular find, by researchers in the UK, China and Germany, represents the most detailed example of a preserved nervous system yet discovered.

̽��ֱ��animal, called Chengjiangocaris kunmingensis, lived during the Cambrian ‘explosion’, a period of rapid evolutionary development about half a billion years ago when most major animal groups first appear in the fossil record. C. kunmingensis belongs to a group of animals called fuxianhuiids, and was an early ancestor of modern arthropods – the diverse group that includes insects, spiders and crustaceans.

“This is a unique glimpse into what the ancestral nervous system looked like,” said study co-author Dr Javier Ortega-Hernández, of the ̽��ֱ�� of Cambridge’s Department of Zoology. “It’s the most complete example of a central nervous system from the Cambrian period.”

Over the past five years, researchers have identified partially-fossilised nervous systems in several different species from the period, but these have mostly been fossilised brains. And in most of those specimens, the fossils only preserved details of the profile of the brain, meaning the amount of information available has been limited.

C. kunmingensis looked like a sort of crustacean, with a broad, almost heart-shaped head shield, and a long body with pairs of legs of varying sizes. Through careful preparation of the fossils, which involved chipping away the surrounding rock with a fine needle, the researchers were able to view not only the hard parts of the body, but fossilised soft tissue as well.

̽��ֱ��vast majority of fossils we have are mostly bone and other hard body parts such as teeth or exoskeletons. Since the nervous system and soft tissues are essentially made of fatty-like substances, finding them preserved as fossils is extremely rare. ̽��ֱ��researchers behind this study first identified a fossilised central nervous system in 2013, but the new material has allowed them to investigate the significance of these finding in much greater depth.

Click to enlarge

̽��ֱ��central nervous system coordinates all neural and motor functions. In vertebrates, it consists of the brain and spinal cord, but in arthropods it consists of a condensed brain and a chain-like series of interconnected masses of nervous tissue called ganglia that resemble a string of beads.

Like modern arthropods, C. kunmingensis had a nerve cord – which is analogous to a spinal cord in vertebrates – running throughout its body, with each one of the bead-like ganglia controlling a single pair of walking legs.

Closer examination of the exceptionally preserved ganglia revealed dozens of spindly fibres, each measuring about five thousandths of a millimetre in length. “These delicate fibres displayed a highly regular distribution pattern, and so we wanted to figure out if they were made of the same material as the ganglia that form the nerve cord,” said Ortega-Hernández. “Using fluorescence microscopy, we confirmed that the fibres were in fact individual nerves, fossilised as carbon films, offering an unprecedented level of detail. These fossils greatly improve our understanding of how the nervous system evolved.”

For Ortega-Hernández and his colleagues, a key question is what this discovery tells us about the evolution of early animals, since the nervous system contains so much information. Further analysis revealed that some aspects of the nervous system in C. kunmingensis appear to be structured similar to that of modern priapulids (penis worms) and onychophorans (velvet worms), with regularly-spaced nerves coming out from the ventral nerve cord.

In contrast, these dozens of nerves have been lost independently in the tardigrades (water bears) and modern arthropods, suggesting that simplification played an important role in the evolution of the nervous system.

Possibly one of the most striking implications of the study is that the exceptionally preserved nerve cord of C. kunmingensis represents a unique structure that is otherwise unknown in living organisms. ̽��ֱ��specimen demonstrates the unique contribution of the fossil record towards understanding the early evolution of animals during the Cambrian period. “ ̽��ֱ��more of these fossils we find, the more we will be able to understand how the nervous system – and how early animals – evolved,” said Ortega-Hernández.

̽��ֱ��research was supported in part by Emmanuel College, Cambridge.

Reference:
Jie Yang et. al. ‘ ̽��ֱ��fuxianhuiid ventral nerve cord and early nervous system evolution in Panarthropoda.’ PNAS (2016). DOI: 10.1073/pnas.1522434113

A 520 million-year-old fossilised nervous system – so well-preserved that individually fossilised nerves are visible – is the most complete and best example yet found, and could help unravel how the nervous system evolved in early animals.

̽��ֱ��more of these fossils we find, the more we will be able to understand how the nervous system – and how early animals – evolved.

Javier Ortega-Hernández

Top: Jie Yang, Bottom: Yu Liu

Top: Complete specimen of Chengjiangocaris kunmingensis from the early Cambrian Xiaoshiba biota of South China. Bottom: Magnification of ventral nerve cord of Chengjiangocaris kunmingensis.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Opinion: Our 500 million-year-old nervous system fossil shines a light on animal evolution

Anonymous — Mon, 29 Feb 2016 16:50:59 +0000

̽��ֱ��nervous system is the command centre of an animal’s body, carrying all the complex electrical signals for the actions that keep it alive, such as moving and eating. Because of its critical function, the nervous system also contains a lot of information about an animal’s evolution, and can even help us understand how different groups relate to each other. But preserved fossilised nervous systems from extinct creatures are extremely rare.

That’s why my colleagues and I were excited to discover one of the most detailed and well-preserved nervous system fossils ever found, from a crustacean-like animal known as a fuxianhuiid that lived more than 500m years ago. These fossils – which come from the Xiaoshiba biota in south China – are so well preserved that you can see individual nerve roots ten times thinner than a human hair. ̽��ֱ��findings offer the most detailed view of the nervous system in early animals available to date, and inform us about the early evolution of the nervous system in these creatures and their close relatives.

Ancient arthropod

̽��ֱ��fuxianhuiids (pronounced foo-see-an-who-eeds) were primitive animals known only to have lived during the early Cambrian period in China, some 515-520m years ago. Fuxianhuiids are widely regarded as being important for understanding the early evolution of the arthropods. This is a large group of animals with jointed limbs and hard exoskeletons that also includes insects, arachnids and crustaceans. So finding preserved nervous tissues in fuxianhuiids tells us a lot about their early evolution and that of their close relatives.

By painstakingly chipping away small pieces of rock from the fossil using a fine needle, my colleagues in China were able to reveal the ventral nerve cord running through their entire body. ̽��ֱ��ventral nerve cord is part of the nervous system, very much similar to our spinal cord, and it resembles a string of beads.

Each of the “beads” actually corresponds to a ganglion, a condensed mass of nerve cells whose function is to control the legs on each segment of the body in fuxianhuiids and other arthropods. Our fossils also preserve dozens of delicate nerves that emerge at either side of the ventral nerve cord and that would have been connected to the legs and other parts of the body.

Ventral cord. Jie Yang (Yunnan ̽��ֱ��, China) (left) and Javier Ortega-Hernández ( ̽��ֱ�� of Cambridge, UK)

Finding the fossilised remains of an animal’s nervous system is extremely unusual, as the brain and ventral nerve cord are mainly made of fatty tissues and decay very quickly under normal circumstances. But under exceptional conditions – such as very rapid burial in environments with little oxygen – these delicate structures can be preserved in the fossil record.

In the last five years, various studies, have reported the preservation of brains in Cambrian arthropods, which has greatly improved our understanding of their evolution. But in most cases, we can only recognise the broad outline of the brain and so there are limits to the information that can be extracted from the fossils. Our study is the first time that a complete ventral nerve cord has been described in such an extraordinary level of detail.

More importantly, the ventral nerve cord of fuxianhuiids is rather unique among arthropods. Whereas most arthropods also posses condensed ganglia, they generally lack the dozens of delicate nerve roots that are found in fuxianhuiids. However, this peculiar organisation can be found in velvet worms (or onychophorans), a group of animals resembling worms with legs that are cousins to the arthropods. So the fuxianhuiid ventral nerve cord is an intermediate between the nervous system of arthropods and velvet worms.

Common ancestral link

This means we can interpret the dozens of nerves in fuxianhuiids as an ancient trait inherited from the last common ancestor between velvet worms and arthropods. This is similar to how the the feet of modern birds resemble the feet of dinosaurs, because they were also inherited from their last common ancestor

By contrast, the presence of ganglia on the nerve cord of fuxianhuiids is an innovation that occurred in the evolution of arthropods. Keeping with the analogy, this is like how feathers are an innovation that occurred in the evolution of birds.

̽��ֱ��most interesting conclusion we can draw is that the origin of the arthropod nervous system required the dramatic reduction in the number of nerves, and that this event took place after the early Cambrian period. Without fuxianhuiids, it would have been impossible to attain this depth of knowledge on the evolution of the nervous system.

Javier Ortega-Hernandez, Research fellow in palaeobiology, ̽��ֱ�� of Cambridge

This article was originally published on ̽��ֱ��Conversation. Read the original article.

̽��ֱ��opinions expressed in this article are those of the individual author(s) and do not represent the views of the ̽��ֱ�� of Cambridge.

Javier Ortega-Hernández (Department of Zoology) discusses what the discovery of the earliest known fossilised nervous system could tell us about evolution.

Top: Jie Yang, Bottom: Yu Liu

Top: Complete specimen of Chengjiangocaris kunmingensis from the early Cambrian Xiaoshiba biota of South China. Bottom: Magnification of ventral nerve cord of Chengjiangocaris kunmingensis.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Spiky monsters: new species of ‘super-armoured’ worm discovered

sc604 — Mon, 29 Jun 2015 19:00:00 +0000

A new species of ‘super-armoured’ worm, a bizarre, spike-covered creature which ate by filtering nutrients out of seawater with its feather-like front legs, has been identified by palaeontologists. ̽��ֱ��creature, which lived about half a billion years ago, was one of the first animals on Earth to develop armour to protect itself from predators and to use such a specialised mode of feeding.

̽��ֱ��creature, belonging to a poorly understood group of early animals, is also a prime example of the broad variety of form and function seen in the early evolutionary history of a modern group of animals that, today, are rather homogenous. ̽��ֱ��results, from researchers at the ̽��ֱ�� of Cambridge and Yunnan ̽��ֱ�� in China, are published today (29 June) in the journal PNAS.

̽��ֱ��creature has been named Collinsium ciliosum, or Hairy Collins’ Monster, named for the palaeontologist Desmond Collins, who discovered and first illustrated a similar Canadian fossil in the 1980s. ̽��ֱ��newly-identified species lived in what is now China during the Cambrian explosion, a period of rapid evolutionary development around half a billion years ago, when most major animal groups first appear in the fossil record.

A detailed analysis of its form and evolutionary relationships indicates that the Chinese Collins’ Monster is a distant early ancestor of modern velvet worms, or onychophorans, a small group of squishy animals resembling legged worms that live primarily in tropical forests around the world.

“Modern velvet worms are all pretty similar in terms of their general body organisation and not that exciting in terms of their lifestyle,” said Dr Javier Ortega-Hernández of Cambridge’s Department of Earth Sciences, one of the paper’s lead authors. “But during the Cambrian, the distant relatives of velvet worms were stunningly diverse and came in a surprising variety of bizarre shapes and sizes.”

̽��ֱ��pattern of diverse ancestors leading to relatively unvaried modern relatives has been observed in other groups in the fossil record, including sea lilies (crinoids) and lamp shells (brachiopods). However, this is the first time that this evolutionary pattern has been observed in a mostly soft-bodied group.

Ortega-Hernández and his colleagues identified a remarkably well-preserved fossil from southern China, which included details of the full body organisation, the digestive tract, even down to a delicate coat of hair-like structures on the front end. Their analysis found it to be a new species – an eccentric ancestor of an otherwise straight-laced group.

̽��ֱ��Chinese Collins’ Monster had a soft and squishy body, six pairs of feather-like front legs, and nine pairs of rear legs ending in claws. Since the clawed rear legs were not well-suited for walking along the muddy ocean floor, it is likely that Collinsium eked out an existence by clinging onto sponges or other hard substances by its back claws, while sieving out its food with its feathery front legs. Some modern animals, including bamboo shrimp, feed in a similar way, capturing passing nutrients with their fan-like forearms.

Given its sedentary lifestyle and soft body, the Chinese Collins’ Monster would have been a sitting duck for any predators, so it developed an impressive defence mechanism: as many as 72 sharp and pointy spikes of various sizes covering its body, making it one of the earliest soft-bodied animals to develop armour for protection.

̽��ֱ��Chinese Collins’ Monster resembles Hallucigenia, another otherworldly Cambrian fossil, albeit one which has been the subject of much more study.

“Both creatures are lobopodians, or legged worms, but the Collins’ Monster sort of looks like Hallucigenia on steroids,” said Ortega-Hernández. “It had much heavier armour protecting its body, with up to five pointy spines per pair of legs, as opposed to Hallucigenia’s two. Unlike Hallucigenia, the limbs at the front of Collins’ Monster’s body were also covered with fine brushes or bristles that were used for a specialised type of feeding from the water column.”

̽��ֱ��spines along Collinsium’s back had a cone-in-cone construction, similar to Russian nesting dolls. This same construction has also been observed in the closely-related Hallucigenia and the claws in the legs of velvet worms, making both Collinsium and Hallucigenia distant ancestors of modern onychophorans. According to Ortega-Hernández, “There are at least four more species with close family ties to the Collins’ Monster, which collectively form a group known as Luolishaniidae. Fossils of these creatures are hard to come by and mostly fragmentary, so the discovery of Collinsium greatly improves our understanding of these bizarre organisms.”

̽��ֱ��fossil was found in the Xiaoshiba deposit in southern China, a site which is less-explored than the larger Chengjiang deposit nearby, but has turned up fascinating and well-preserved specimens from this key period in Earth’s history.

“Animals during the Cambrian were incredibly diverse, with lots of interesting behaviours and modes of living,” said Ortega-Hernández. “ ̽��ֱ��Chinese Collins’ Monster was one of these evolutionary ‘experiments’ – one which ultimately failed as they have no living direct ancestors – but it’s amazing to see how specialised many animals were hundreds of millions of years ago. At its core, the study of the fossil record seeks answers about the evolution of life on Earth that can only be found in deep time. All the major biological events responsible for shaping the world we inhabit, such as the origin of life, the early diversification of animals, or the establishment of the modern biosphere, are intimately linked to the complex geological history of our planet.”

̽��ֱ��research was funded by the National Natural Science Foundation of China, Emmanuel College, Cambridge, and the Templeton World Charity Foundation.

A newly-identified species of spike-covered worm with legs, which lived 500 million years ago, was one of the first animals on Earth to develop armour for protection.

Collins’ Monster sort of looks like Hallucigenia on steroids

Javier Ortega-Hernández

Left: Jie Yang. Right: Javier Ortega-Hernández

Collinsium ciliosum, a Collins’ monster-type lobopodian from the early Cambrian Xiaoshiba biota of China

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Clues contained in 500 million-year-old brain point to the origin of heads in early animals

sc604 — Thu, 07 May 2015 16:00:01 +0000

A new study from the ̽��ֱ�� of Cambridge has identified one of the oldest fossil brains ever discovered – more than 500 million years old – and used it to help determine how heads first evolved in early animals. ̽��ֱ��results, published today (7 May) in the journal Current Biology, identify a key point in the evolutionary transition from soft to hard bodies in early ancestors of arthropods, the group that contains modern insects, crustaceans and spiders.

̽��ֱ��study looked at two types of arthropod ancestors – a soft-bodied trilobite and a bizarre creature resembling a submarine. It found that a hard plate, called the anterior sclerite, and eye-like features at the front of their bodies were connected through nerve traces originating from the front part of the brain, which corresponds with how vision is controlled in modern arthropods.

̽��ֱ��new results also allowed new comparisons with anomalocaridids, a group of large swimming predators of the period, and found key similarities between the anterior sclerite and a plate on the top of the anomalocaridid head, suggesting that they had a common origin. Although it is widely agreed that anomalocaridids are early arthropod ancestors, their bodies are actually quite different. Thanks to the preserved brains in these fossils, it is now possible to recognise the anterior sclerite as a bridge between the head of anomalocaridids and that of more familiar jointed arthropods.

“ ̽��ֱ��anterior sclerite has been lost in modern arthropods, as it most likely fused with other parts of the head during the evolutionary history of the group,” said Dr Javier Ortega-Hernández, a postdoctoral researcher from Cambridge’s Department of Earth Sciences, who authored the study. “What we’re seeing in these fossils is one of the major transitional steps between soft-bodied worm-like creatures and arthropods with hard exoskeletons and jointed limbs – this is a period of crucial transformation.”

Ortega-Hernández observed that bright spots at the front of the bodies, which are in fact simple photoreceptors, are embedded into the anterior sclerite. ̽��ֱ��photoreceptors are connected to the front part of the fossilised brain, very much like the arrangement in modern arthropods. In all likelihood these ancient brains processed information like in today’s arthropods, and were crucial for interacting with the environment, detecting food, and escaping from predators.

During the Cambrian Explosion, a period of rapid evolutionary innovation about 500 million years ago when most major animal groups emerge in the fossil record, arthropods with hard exoskeletons and jointed limbs first started to appear. Prior to this period, most animal life on Earth consisted of enigmatic soft-bodied creatures that resembled algae or jellyfish.

These fossils, from the collections of the Royal Ontario Museum in Toronto and the Smithsonian Institution in Washington DC, originated from the Burgess Shale in Western Canada, one of the world’s richest source of fossils from the period.

Since brains and other soft tissues are essentially made of fatty-like substances, finding them as fossils is extremely rare, which makes understanding their evolutionary history difficult. Even in the Burgess Shale, one of the rare places on Earth where conditions are just right to enable exceptionally good preservation of Cambrian fossils, finding fossilised brain tissue is very uncommon. In fact, this is the most complete brain found in a fossil from the Burgess Shale, as earlier results have been less conclusive.

“Heads have become more complex over time,” said Ortega-Hernández, who is a Fellow of Emmanuel College. “But what we’re seeing here is an answer to the question of how arthropods changed their bodies from soft to hard. It gives us an improved understanding of the origins and complex evolutionary history of this highly successful group.”

̽��ֱ��research is supported by Emmanuel College, Cambridge.

̽��ֱ��discovery of a 500 million-year-old fossilised brain has helped identify a point of crucial transformation in early animals, and answered some of the questions about how heads first evolved.

This is a period of crucial transformation

Javier Ortega-Hernández

Jean Bernard Caron, Royal Ontario Museum

Odaraia alata, an arthropod resembling a submarine from the middle Cambrian Burgess Shale.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Misunderstood worm-like fossil finds its place in the Tree of Life

sc604 — Sun, 17 Aug 2014 17:00:00 +0000

̽��ֱ��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 ̽��ֱ�� 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. ̽��ֱ��results are published in the advance online edition of the journal Nature.

̽��ֱ��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. ̽��ֱ��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. ̽��ֱ��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. ̽��ֱ��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 ̽��ֱ��’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.”

“ ̽��ֱ��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.

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.

̽��ֱ��spines along its back were thought to be legs, its legs thought to be tentacles along its back, and its head was mistaken for its tail.

M. R. Smith / Smithsonian Institute

Fossil Hallucigenia sparsa from the Burgess Shale

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