An ancient time that animals forgot

Apologies for the lack of Bad Casts these last few weeks. I recently set up a new joint blog with some Twitter pals called Twilight Beasts which looks at the world of Ice Age animals. As the blog looks at creatures that lived only a short while ago, I thought this weeks Bad Cast should go back, right back to when the first big organisms ruled. Don’t worry, there are plenty of bad casts that link to Twilight Beasts. But they can wait.

Thank you for the prompts for me to get another lot of posts on Bad Casts up. (Well, the thank you is to the one person who desperately wanted to see some more, my brother in law. Steve, this one’s for you.)

This bad cast looks like a 16 century illustration of the Sun. There was no museum number with it (which is a really important number we need to find information). The only thing written on the label was ‘fossil jellyfish’. Nice and helpful. Our predecessors have an awful lot to answer for.

The shading is nice. Pity the creature looks like an early drawing of the sun.

The shading is nice. Pity the creature looks like an early drawing of the sun.

 

Some readers may recognise it. It looks like it is a cast of a very cool, very old fossil. Around 530 million years ago (during a time called the Cambrian Period) there appears to have been a sudden explosion of life on our planet. Some sedimentary rocks of this age hold some incredibly beautiful, and bizarre, fossils of creatures  (such as the incredible Burgess Shale). What makes these fossils so incredible is that the rocks before them (that’s 4 billion years worth), don’t contain complex, big animals. There are some microfossils, stromatolites and other oddities, but nothing like the terrifying giant Anomalocaris. The beginning of the Cambrian Period is called the Cambrian Explosion, where all the major groups of animals can be found. This appeared out of the blue, in a relatively short time of 20 million years (this is a blink in geological time!). Scientists think that evolution sped up during this time due to change in chemistry in the waters, predator-prey interaction, or perhaps the evolution of eyes.

Before this, around 650 million years ago, there was a strange time on the planet. The lands were rocky and barren. The waters held millions of microorganisms, but also something else. Something weird.

Strange impressions in very old rocks had been found in sites in Africa, Newfoundland and Australia. But these were thought to be Cambrian fossils, and even then the fossils were not very clear. Some were discovered in Charnwood Forest, in Leicestershire, which changed everything. The rocks of England were very well mapped, so the age of the rocks was known with a lot of confidence. It was clear that the rocks at Charnwood were older than the Cambrian, and went back into the vastness of time which is cleverly called the Precambrian (this covers the rest of Earth’s history from the beginning of the Cambrian 530 million years ago to around 4 billion years).

The Charnwood fossils, and those of Africa, Newfoundland and Australia were all from around 650 million years ago, and are the earliest large organisms so far discovered. A huge variety of different impressions have been found, and collectively are called the Ediacara Biota (after the Ediacara Hills in Australia which contained hundreds of specimens).

The fossils are of some of the strangest organisms that have lived. (I keep saying ‘organisms’ instead of ‘animal’ or ‘plant’ because they could be wither, scientists are still arguing over what they could possibly be.) There are disc shaped ones (like or bad cast), long leaf-like ones, flat trilobite ones and ones that don’t resemble anything. It is thought that the disc shaped ones were actually the base for the leaf shaped ones, so they held them in place in the waters.

Nice an colourful reconstruction of the seas around 650 million years ago.

Nice an colourful reconstruction of the seas around 650 million years ago. (Image from here)

In fairness to this bad cast, the fossil itself isn’t exactly spectacular. Which begs the obvious question, why have a cast of it? Our little circle sun plaster cast could be the ‘holdfast’ for a sea-pen on the sea floor, millions of years before the oceans were teeming with the ancestors of all life today. Some scientists think that the Ediacara organisms may have been a dead end; they were not the ancestors to anything and they just simply flourished for a time, and then died out. It was a very interesting time on the planet where a little snorkelling trip would have revealed a completely alien world with things that you wouldn’t recognise. But a beautiful alien world it most surely was.

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