Algae? Fungi? Some other type of plant? The Ediacaran organisms, ancient life forms that were common on in the Earth's oceans half a billion years ago, have puzzled scientists for decades. Now two paleontologists feel confident that the ancient species were something completely different: animals that were unlike any seen on Earth today.

Scientists have discovered nearly 200 different types of Ediacarans within ancient rocks around the globe since the first discovery in the 1940s. It's easy to identify an Ediacaran through their unique bodies, which are branched fronds taking the shape of fractals. Looking like long tubes that could grow up to six feet, Ediacaran fronds also had sub-fronds which replicated these patterns.

It's easy to mistake an Ediacaran for a plant. But Jennifer Hoyal Cuthill at the Tokyo Institute of Technology and the University of Cambridge in the United Kingdom, along with Jian Han at Northwest University in Xi’an, China, has found evidence that says otherwise. They came to their conclusion through studying Stromatoveris psygmoglena, a marine species first discovered in 2006 that dates back to around 30 million years after Ediacarans supposedly died out.

A Stromatoveris fossil. HOYAL CUTHILL

Cuthill and Han argue that S. psygmoglena was actually a hardy Ediacaran, holding on to life while the rest of the species died out. After studying 200 samples of the S. psygmoglena found in southwestern China, Cuthill began to see the similarities. Like the Ediacarans, these tiny animals shared several repeated, branched fronds with a fractal internal architecture. "I began thinking: My goodness, I’ve seen these features before,” she recounts in a press statement.

Looking to classify their animals into a phylum, Hoyal Cuthill and Han ran a computer analysis using anatomical features to reconstruct evolutionary relationships. But they came up blank. It seems that these creatures belong to a completely unique phylum, somewhere between sponges and more complex animals with digestive cavities like worms.

With one question about Ediacarans answered, several more pop up: How did they die out? How did S. psygmoglena survive? These questions had previously been settled, with the Cambrian explosion being the answer. If Ediacarans were plants, they died out after the Cambrian explosion brought forth animal life on an unprecedented scale to the planet. But if that's not the case, what exactly happened?

“It’s not quite so neat anymore,” Cuthill says. “As to what led to their eventual extinction I think it’s very hard to say.” The curious case of the Ediacaran will live on for another day.



Source: Science

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