Evolution: earliest eukaryote diverse fossils (Evolution)

by David Turell , Friday, January 26, 2024, 16:33 (91 days ago) @ David Turell

Another paper on the subject:

https://www.sciencemagazinedigital.org/sciencemagazine/library/item/26_january_2024/416...

"Prokaryotes evolved first, up to 3.9 billion years ago; within a few hundred million years, some of them, the cyanobacteria, began to form chains of cells, considered an advance in life’s complexity. About 2 billion years ago, much larger, single-cell eukaryotes bearing nuclei showed up. For decades, researchers thought eukaryotes didn’t form simple multicellular structures until 1 billion years after they arose, and that once chain structures evolved, more elaborate body plans—animals with organs—appeared soon after. “There was this perception that multicellularity was hard [to evolve],” Travisano says.

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"In this week’s paper, they report that the fossils consist of strings of up to 20 cylindrical cells, with adjoining cell walls, like plants, visible under a microscope as dark rings. Several fossils had spores—with their own cell walls—suggesting the filaments had specialized reproductive structures.

“'What’s striking about these fossils is they are really rather enormous for that age, and they are multicellular,” says Jochen Brocks, an organic geochemist at Australian National University.

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"Miao performed chemical tests on the fossils and found the structures of their organic carbon compounds were different from those in cyanobacteria fossils in these rocks. Her team concluded the filaments were most likely green algae, similar to modern eukaryotes such as Urospora wormskioldii.

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"The new findings build on work Bengtson and colleagues reported in 2017, when they proposed that 1.6-billion-year-old fossils found in India represented red algae. In 2021, another team described “walled microfossils,” which they interpreted as a diverse set of eukaryotes, in deposits from Canada dating back 1.57 billion years. And just last month, Leigh Anne Riedman and Susannah Porter, paleontologists at the University of California, Santa Barbara, and colleagues described what they say are several eukaryotic fossils found in 1.642-billion-year-old rocks from Australia.

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"If simple but diverse multicellular forms appeared so early, then complex multicellularity took a lot longer to evolve than most researchers had thought; the first creatures with organs and cells that did not have direct access to the outside environment didn’t appear until less than 1 billion years ago. Such a delayed timeline makes sense to Shuhai Xiao, a geobiologist and a paleobiologist at the Virginia Polytechnic Institute and State University. Truly complex eukaryotes “have multiple cells that stay together, communicate with each other, and have different sizes, shapes, and functions,” he explains. “It takes time [to make such advances].'” (my bold)

Comment: note my bold. The next major advanced was the Cambrian animals at 5.4 million years ago.