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946.   Fóssil Exibe Evolução do Sistema Nervoso













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Fuxianhuiid ventral nerve cord and early nervous system evolution in Panarthropoda

Significance

  Understanding the evolution of the CNS is fundamental for resolving the phylogenetic relationships within Panarthropoda (Euarthropoda, Tardigrada, Onychophora). The ground pattern of the panarthropod CNS remains elusive, however, as there is uncertainty on which neurological characters can be regarded as ancestral among extant phyla. Here we describe the ventral nerve cord (VNC) in Chengjiangocaris kunmingensis, an early Cambrian euarthropod from South China. The VNC reveals extraordinary detail, including condensed ganglia and regularly spaced nerve roots that correspond topologically to the peripheral nerves of Priapulida and Onychophora. Our findings demonstrate the persistence of ancestral neurological features of Ecdysozoa in early euarthropods and help to reconstruct the VNC ground pattern in Panarthropoda.

Abstract

  Panarthropods are typified by disparate grades of neurological organization reflecting a complex evolutionary history. The fossil record offers a unique opportunity to reconstruct early character evolution of the nervous system via exceptional preservation in extinct representatives. Here we describe the neurological architecture of the ventral nerve cord (VNC) in the upper-stem group euarthropod Chengjiangocaris kunmingensis from the early Cambrian Xiaoshiba Lagerstätte (South China). The VNC of C. kunmingensis comprises a homonymous series of condensed ganglia that extend throughout the body, each associated with a pair of biramous limbs. Submillimetric preservation reveals numerous segmental and intersegmental nerve roots emerging from both sides of the VNC, which correspond topologically to the peripheral nerves of extant Priapulida and Onychophora. The fuxianhuiid VNC indicates that ancestral neurological features of Ecdysozoa persisted into derived members of stem-group Euarthropoda but were later lost in crown-group representatives. These findings illuminate the VNC ground pattern in Panarthropoda and suggest the independent secondary loss of cycloneuralian-like neurological characters in Tardigrada and Euarthropoda.

Fonte : PNAS, 01/03/2016

Autor : Javier Ortega-Hernández,...

Referência : doi:10.1073/pnas.1522434113



The Oldest Fossilised Nervous System Ever Found

520 million-year-old remains are so detailed they feature individual NERVES

  More than half a billion years ago, scurrying along the ocean floor, an ancient relative of modern day creepy crawlies gave its final twitch as it died.

  Now, 520 million years later, a team of archaeologists which uncovered its remains believe it to be one of the oldest and most detailed fossilised nervous systems from the period ever found. 

  Its fossilised remains have been so well preserved that individual nerves can be seen, providing scientists with new insight into how the systems of insects, crabs and spiders, have evolved.

  The crustacean-like creature, called Chengjiangocaris kunmingensis, belonged to a group of animals called the fuxianhuiids, which were early ancestors of modern arthropods.

  It lived during the Cambrian explosion, a period of rapid evolutionary development when the first major animal groups are believed to have emerged.

  'This is a unique glimpse into what the ancestral nervous system looked like,' said Dr Javier Ortega-Hernández, of the University of Cambridge's Department of Zoology and co-author of the study.

  'It's the most complete example of a central nervous system from the Cambrian period.'  

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

  The central nervous system in arthropods consists of a condensed brain and a chain-like series of interconnected masses of nervous tissue that resemble a string of beads.

  Preparation of the fossils involves chipping away at the surrounding rock with a fine needle, with researchers then able to view the hard body parts and fossilised soft tissue.

  The nervous system and soft tissues are essentially made of fatty-like substances so finding them preserved as fossils is extremely rare.

  The exceptionally well-preserved nerve cord of C.kunmingensis represents a unique structure that is otherwise unknown in living organisms, with the researchers saying it shows just how important the fossil record is in understanding the evolution of animals in the period.

  A closer look at the animal's fossil revealed tiny fibres just five thousandths of a millimetre long, branching out at regular intervals.

  '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 Dr Ortega-Hernández. 

  Analysis using fluorescence microscopy showed that they were in fact nerves, offering 'an unprecedented level of detail'.

  Dr Ortega-Hernández added: 'These fossils greatly improve our understanding of how the nervous system evolved.'

  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.

  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.

  Researchers first identified a fossilised central nervous system in 2013 but the new material has allowed them to investigate the significance of these findings in much greater depth.

  The findings, published in the journal Proceedings of the National Academy of Sciences, are helping researchers understand how the nervous system of creepy crawlies with jointed legs evolved.

WHAT SPURRED THE CAMBRIAN EXPLOSION 542 MILLION YEARS AGO?

  The 'Cambrian explosion' began roughly 542 million years ago after the end of the Ediacaran Period.

  During this time, large numbers of complex animal species emerged.

  Researchers argue many possible causes for the Cambrian explosion, from the rise of atmospheric oxygen to the rise in carnivorous species.

  What has largely been accepted as the second oxygenation event during the Late Neoproterozoic Era from 750 to 540 million years ago is thought to have continued the process of oxygenating Earth's atmosphere.

  Some scientists believe this gave rise to the 'Cambrian explosion,' of 540-520 million years ago that birthed diverse animal groups.

  But, a new hypothesis suggests the evolutionary changes may have stemmed from the reversals of Earth's magnetic field.

  A reversal period can occur over 7000-10,000 year, weakening the ozone layer between 20 and fourty percent in some areas, and allowing in more harmful solar radiation and cosmic rays.

  With UV radiation pouring in, animals that could escape the light would have a much more favourable chance of survival.

  Hard shells and complex eyes would allow organisms to seek shelter and burrow deeply, facilitating the 'flight from light.'

  And, it would allow these animals to thrive in deeper areas with stronger waves. 

Fonte : Daily Mail, 01/03/2016

Autor : Harriet Mallinson, Ryan O’Hare

Scientists who have uncovered an ancient fossilised relative of modern day arthropods say it is the most complete example of a central nervous system from the Cambrian period, 520 million years ago

The image shows a complete fossilised specimen of C.kunmingensis (top) and a reconstruction of its body (bottom). A closer look at the animal's fossil revealed tiny fibres just five thousandths of a millimetre long, branching out at regular intervals, which analysis showed to be nerves

The nervous system and soft tissues are essentially made of fatty-like substances so finding them preserved as fossils is extremely rare

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