A Cambrian nervous system, fossilised #FossilFridayThings tended to preserve better in the early day

A Cambrian nervous system, fossilised #FossilFridayThings tended to preserve better in the early days of large multicellular life’s great bush, partly because the great variety of burrowing creatures were still thin on the ground, and they often destroy the remnants of organisms before they can fossilise (a process known as taphonomy). Back in them days the dominant creatures were arthropods, the phylum that includes insects, arachnids (spiders and scorpions) and crustacea (shrimp, lobster, crabs etc). A series of fossils from China dated to 520 million years ago have turned out to have such exceptional preservation that the nervous system is visible, making them the oldest and most complete found so far, and they offer a critical insight into the development of crustacean brains. Fossilised soft tissues are very rare, only being preserved in exceptional and uncommon geological circumstances. A few years back most paleontologists would not have believed such finds possible. Some exceptional sites did assemble these conditions, and are crucial to expanding our knowledge beyond the bones and teeth that form most fossils. Known as Chengjiangocaris kunmingensis, the fossil was first reported 3 years back, but detailed examination is revealing marvellous things. They found the main nerve chord, and the ganglia of cells that would have controlled each individual pair of legs (out of 80), said assemblage being similar to that found today. However they also discovered many more nerve roots branching off from the chord than their modern descendants, showing how simplification and efficiency have been part of this structure’s long evolution. The pathways of individual nerves could be traced through the organism. The main brains are missing sadly, since shrimp heads often part from the body after death, but there’s plenty more mudstone in the formation, and one might turn up any time. .The 5-15 cm fossils come from shales in central China, the lithified remnants of dark organic rich anoxic marine mudstones, and the nervous systems are preserved as flat carbon films (the remnants of the fats in the brain), sometimes with pyrite crystals. The creatures were entombed in the sediment by a submarine landslide, preventing decay and scavenging and then compressed and dewatered by the weight of additional sediment being deposited above. Luckily arthropods have the densest nervous tissue of any animal, which also helped it to survive the aeons. Preparation was tough without damaging the structures, and involved much painstaking chipping of flakes of mudstone with a fine needle using a stereo microscope (for more on this amazing work see http://on.fb.me/1PPOiTc).Here’s hoping for many more interesting specimens from the Chengjiang biota, which provide a similar window on the Cambrian world to the more famous Burgess Shale (see http://on.fb.me/1UylWiD), but some 20 million years older..LozImage credit: Jie Yang (Yunnan University, China)http://bit.ly/1LQDb7J: http://bit.ly/1TRBcq8http://bit.ly/21CrgXwhttp://bit.ly/1SeIKTWhttp://bit.ly/1oYgbyYhttp://bit.ly/1oOPlZrhttp://bit.ly/217U44OOriginal papers, paywall access: http://bit.ly/1LwNDGC, http://bit.ly/1L5r8Ze -- source link
Tumblr Blog : the-earth-story.com

More pics about