Evolution: earliest eukaryote diverse fossils (Evolution)

by David Turell , Sunday, January 14, 2024, 19:45 (104 days ago) @ David Turell

Back to 1.64 million years ago:

https://www.sciencedaily.com/releases/2024/01/240111162731.htm

"In a new account of exquisitely preserved microfossils, researchers at UC Santa Barbara and McGill University revealed that eukaryotic organisms had already evolved into a diverse array of forms even 1.64 billion years ago. The paper, published in the journal Papers in Paleontology, recounts an assemblage of eukaryotic fossils from an era early in the group's evolutionary history. The authors describe four new taxa, as well as evidence of several advanced characteristics already present in these early eukaryotes.

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"The researchers were surprised by the diversity and complexity preserved in these fossils. They recorded 26 taxa, including 10 previously undescribed species. The team found indirect evidence of cytoskeletons, as well as platy structures that suggest the presence of internal vesicles in which the plates were formed -- perhaps ancestral to Golgi bodies, present in modern eukaryotic cells. Other microbes had cell walls made of bound fibers, similarly suggestive of the presence of a complex cytoskeleton.

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"The authors also found cells with a tiny trapdoor, evidence of a degree of sophistication. Some microbes can form a cyst to wait out unfavorable environmental conditions. In order to emerge, they need to be able to etch an opening in their protective shell. Making this door is a specialized process. "If you're going to produce an enzyme that dissolves your cell wall, you need to be really careful about how you use that enzyme," Riedman said. "So in one of the earliest records of eukaryotes, we're seeing some pretty impressive levels of complexity."

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"A big part of this effort involves understanding when different characteristics of eukaryotes first arose. For instance, the authors are quite interested to learn whether these organisms were adapted to oxygenated or anoxic environments. The former would suggest that they had an aerobic metabolism, and possibly mitochondria. Every modern eukaryote that's been found descends from ancestors that possessed mitochondria. This suggests that eukaryotes acquired the organelle very early on, and that it provided a significant advantage.

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"'These results are a directive to go look for older material, older eukaryotes, because this is clearly not the beginning of eukaryotes on Earth," Riedman said."

Comment: eukaryotes are highly complex organisms who needed to develop an oxidated metabolism to advance. Acquiring mitochondria was a vital design step. Not by chance.