Evolution: a mass extinction in the Ediacaran (Introduction)

by David Turell , Thursday, November 10, 2022, 18:32 (742 days ago) @ David Turell

Just discovered:

https://www.sciencealert.com/scientists-uncover-evidence-of-what-may-be-earths-first-ma...

"Researchers from the US have uncovered evidence of one occurring earlier, around 550 million years ago during a period known as the Ediacaran.

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"Because softer body parts typically don't fossilize as readily as harder, more mineralized bits of anatomy, researchers have typically suspected a relative absence of soft-bodied animals in the Ediacaran's later stages are simply the result of a failure to be preserved.

"But the global fossil record indicates otherwise.

"The team found that there was an overall increase in biodiversity between the earlier and middle stages of the Ediacaran, known as the Avalon (575 to 560 million years ago) and White Sea stages (560 to 550 million years ago).

"'We find significant differences in the feeding mode, life habit, ecological tier, and maximum body size between the Avalon and White Sea assemblages," the team writes in their paper.

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"All types of feeding modes and life habits experienced similar losses, with only 14 genera still seen in the Nama out of 70 known groups from the earlier White Sea stage. If more newly evolved species had taken over, there also would have been temporal overlap between the new and the old species. This wasn't observed, the team argue, ruling out biotic replacement.

"'The decline in diversity between these assemblages is indicative of an extinction event, with the percentage of genera lost comparable to that experienced by marine invertebrates during the 'Big 5' mass extinctions," Evans and colleagues write.

"Many of the White Sea animals that survived the extinction event and remained in the Nama period were large, frond-like organisms with a high surface area to volume ratio. This could be a sign these animals were adapting to deal with a reduction in oceanic oxygen.

"'By maximizing the relative proportions of cells in direct contact with seawater, high surface-area taxa would have been comparatively better adapted to survive in low-oxygen environments," the team explains.

"There is also recent geochemical evidence to support this idea, with a 2018 study finding signs of extensive ocean anoxia that covered more than 20 percent of the seafloor at the end of the Ediacaran.

"'Thus, our data support a link between Ediacaran biotic turnover and environmental change, similar to other major mass extinctions in the geologic record," the team concludes."

Comment: not a surprising finding considering the other major events. Note the new ease of finding 'soft body' forms