New Ediacaran fossils; a segmented worm and burrow (Introduction)

by David Turell , Thursday, September 05, 2019, 18:09 (1696 days ago) @ David Turell

A segmented bilaterian that could move and burrow:

https://www.nature.com/articles/d41586-019-02556-x?utm_source=Nature+Briefing&utm_c...

"More than half a billion years ago, a strange, worm-like creature died as it crawled across the muddy sea floor. Both the organism and the trail it left lay undisturbed for so long that they fossilized. Now, they are helping to revise our understanding of when and how animals evolved.

"The fossil, which formed some time between 551 million and 539 million years ago, in the Ediacaran period, joins a growing body of evidence that challenges the idea that animal life on Earth burst onto the scene in an event known as the Cambrian explosion, which began about 539 million years ago.

“'It is just pushing things further and further back into the Ediacaran,” says Rachel Wood, a geoscientist at the University of Edinburgh, UK. The Cambrian explosion no longer appears to be such an abrupt event in the history of life on Earth, she says. An analysis of the fossil, along with a few dozen similar specimens found in the same rock sequence in southern China, is published in Nature1.

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" ...it’s exceptionally rare to find a dead animal preserved at the end of a trail it made when alive, he says. Second, the fossil dates to a crucial moment in the evolution of animal life.
And third: “It’s such a bizarre-looking organism,” says Darroch. The creature, which has been named Yilingia spiciformis and was up to 27 centimetres long, seems to be a biologically complex animal with a distinct front and rear end. “We don’t really have many of those from the Ediacaran,” he says.

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"Some Ediacaran organisms have been recognized as animals despite their peculiar anatomy, which suggests that animal life began millions of years before the Cambrian explosion.

"Yilingia spiciformis fits into that picture and pushes the idea further. With a segmented body that is symmetrical down its length, it has an anatomy that is more obviously similar to that of Cambrian animals, says Shuhai Xiao, a palaeontologist at Virginia Tech in Blacksburg and a co-author of the study.

"What’s more, the trail demonstrates that Y. spiciformis could crawl over the sea floor like a modern animal. Palaeontologists have found only few pieces of evidence that the strange organisms of the Ediacaran were similarly mobile. Collectively, Xiao’s team’s findings mean that Y. spiciformis looked and behaved like a Cambrian animal — despite living up to 12 million years before what is usually considered the start of the Cambrian explosion.

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"Exactly which animal lineage Y. spiciformis belonged to is unclear. The researchers suggest it might be a relative of insects and crustaceans such as shrimp and lobsters, because it seems to have leg-like structures. If further analysis shows that those structures are actually an artefact of the fossilization process, the animal might instead be some sort of primitive segmented worm.

“'There’s a third possibility,” says Xiao: it could be an ancestor to both groups. The idea that segmented worms and shrimp-like creatures all evolved from a single group of segmented animals dates back to the nineteenth century, but it’s controversial because most researchers now think that shrimp-like animals are more closely related to nematode worms and other creatures that grow by shedding an exoskeleton."

Comment: Certainly this animal is an early 'real animal', compared to the weird Ediacaran forms that might be animals. It is nowhere as complex as Cambrian species despite efforts of the author to close the Cambrian Explosion gap. I would suspect some early transitional forms between Ediacaran and Cambrian eras, as this simple one appears to be.