New Ediacaran fossils; new more advanced forms (Introduction)

by David Turell , Wednesday, October 28, 2020, 21:30 (1487 days ago) @ David Turell

Have some m ore advance in organ systems:

https://www.nature.com/articles/d41586-020-02985-z?utm_source=Nature+Briefing&utm_c...

"Palaeontologist Shuhai Xiao marvels at the tracks left by this creature, Yilingia spiciformis, and how they captured evidence of its movement. In his cluttered office at Virginia Tech in Blacksburg, he shows off a slab of beige resin — a reproduction of the fossil, which was found in China’s Yangtze Gorges region and is now kept in a Chinese research institute. The replica captures a snapshot of a moment from 550 million years ago. Xiao, whose team formally described Yilingia last year1, traces the bumpy tracks it made immediately before its death.

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"Yilingia is not the only creature from that region to provide some of the earliest fossil evidence for an important animal feature. In 2018, Xiao and his team reported2 on tracks found in the Yangtze Gorges consisting of two parallel rows of dimples. The researchers propose that the trails were made by an animal from 550 million years ago that might have been able to burrow and had multiple pairs of appendages — which would make it one of the earliest-known animals with legs.

"These Chinese fossils hail from a time right before the Cambrian explosion, the evolutionary transformation when most of the animal groups that populate the planet today first made their appearance in the fossil record. Scientists long regarded the boundary between the Cambrian period and the Precambrian as a dividing point in evolution — a transition from a world in which simple, strange organisms flourished, to a time when the seas teemed with complex creatures that are the forebears of nearly everything that followed.

"But a growing number of findings reveal that the time slice just before the Cambrian, known as the Ediacaran (635 million to 541 million years ago), was a pivot point of animal evolution — a period that includes the earliest fossil records of anatomical innovations, such as guts and legs, and the first appearance of complex behaviours such as burrowing. The insights into the Ediacarans’ powers lend support to a provocative idea: that the Cambrian explosion, that iconic evolutionary burst, was actually less revolutionary than many had thought.

"The Cambrian explosion “is just another phase of evolution”, says palaeobiologist Rachel Wood at the University of Edinburgh, UK. “It’s not a single flash event. It could not have happened without previous waves of innovation.”

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"Now, most scientists are reaching agreement that the Ediacarans were a grab bag of disparate life forms, rather than the self-contained group proposed by Seilacher. “It’s inappropriate to consider them a failed experiment,” says palaeontologist Frances Dunn at the University of Oxford, UK. “They represent the ancestors, probably, of lots of different things.” Many scientists — although not all — are also signing up to the idea that some fraction of the Ediacaran organisms were probably animals, including some that don’t look like any animal alive today.

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"More evidence that Ediacarans had guts comes from tubular organisms called cloudinids that arose around 550 million years ago. Using high-resolution X-ray imaging to peer inside cloudinids’ outer tubes, researchers saw a long, cylindrical feature, which the authors say is the oldest gut in the fossil record8. The team found this feature in a cloudinid that most probably belonged to the genus Saarina, and it bolsters the case that some cloudinids were animals with left–right symmetry8, says palaeobiologist and study co-author Jim Schiffbauer at the University of Missouri, Columbia. The gut’s shape and other clues hint that Saarina could be an early annelid, an animal grouping that includes modern earthworms.

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"The burst of new species in the Cambrian “didn’t just come out of thin air”, says Wood. “It must have been derived from something in the Ediacaran.”

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All of these findings tell a new story of animal evolution — but it is not yet clear whether the revision will stick. Some palaeontologists say that Wood’s argument, in trying to give the Ediacaran its due, gives short shrift to the Cambrian explosion — which marked the appearance of a vast number of creatures that fit clearly into modern animal groups. Xiao agrees that some Ediacaran animals survived into the Cambrian, but he argues that the big picture shows a mass die-off at the boundary between the two periods. And invertebrate palaeontologist Jean-Bernard Caron at the Royal Ontario Museum in Toronto, Canada, questions Wood’s tally of Ediacaran species that survived into the Cambrian. “We don’t really have the fossil record to support that,” he says. Wood responds that although the critique is fair, it’s clear that multiple Cambrian-style creatures first appeared in the Ediacaran.

Comment: A very important paper. As I view it, some complexity arising in the Ediacaran is not a surprise, but sehatg has been found is still a giant step away from the very complex Cambrian forms that are our precursors. Note the objections above warning not to overinterpret the new findings.