̽��ֱ�� of Cambridge - Yunnan ̽��ֱ��

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.

Yes

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

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

Yes