Our earliest microbial ancestors were ahead of their time

Before Neanderthals and Denisovans, before human-like primates, or proto-mammals, or fish that crawled out of the ocean to become the first land animals, our first ancestors were microbes.

More complex organisms like us descend from eukaryotes, which have a nuclear membrane around their DNA (unlike prokaryotes, which do not). It was believed that eukaryotes had Evolved A few billion years ago, during the Late Paleolithic period, they began to diversify about 800 million years ago. Its diversity was not well understood. Now, a team of researchers led by paleontologist Lee Ann Redman of the University of California, Santa Barbara, has discovered eukaryotic microfossils that are 1.64 billion years old, but were already diverse and had surprisingly complex features.

“High levels of eukaryotic species richness and morphological variation indicate that although the Late Paleolithic [fossils] “In order to preserve our oldest record of eukaryotes, the clade of eukaryotes has a much deeper history,” Redman and her team said in a report. Stady Recently published in Papers in Paleontology.

Really, really, really old tricks

During the late Paleoproterozoic, eukaryotes likely evolved following several major changes on Earth, including a large increase in atmospheric oxygen and shifts in ocean chemistry. This could be anywhere from 3 billion to 2.3 billion years ago. Redman's team explored sedimentary rock layers in the Limbonia region in Australia's Berndudoo Basin. The fossils they discovered included a total of 26 species, in addition to 10 species that had not been described before. One of them is Limbunyasphaera operculata, A kind of new sex Limboniasphyra.

What does it make? L.operculata It is very special that it has a feature that appears to be evidence of a survival mechanism used by modern eukaryotes. There are some microbes present that make up A Protective bag So that they can overcome harsh conditions. As things become more tolerable, they produce an enzyme that dissolves part of the cyst wall into an opening, or pus, allowing it to crawl out. This slot also has a cover or lid. These two things were observed in L.operculata.

While divisions in fossilized unicellular organisms may be the result of pitting processes that break down the cell wall, complex structures such as the pylorus and operculum are not found in prokaryotic organisms, thus indicating that the species must be eukaryotic.

I didn't know they could do that

Some previously known species of extinct eukaryotes have also surprised scientists with unexpected advanced features. Satka vavusa It has a vesicle in the cell surrounded by a membrane with lamellar structures. another type, perindodotoba brigandeniya, Plates were also identified around their vesicles, although none of their lamellae were as diverse in shape as those seen in different forms. S. favosa Individually. These paintings came in a large variety of shapes and sizes, which may mean what they were named S. favosa It is more than one type.

Coated vesicle S. favosa This led Redman to determine that this species must be eukaryotic, because laminae are possible indicators of the presence of Golgi bodies in these organisms. After the cell's endoplasmic reticulum synthesizes proteins and lipids, Golgi bodies process and package these materials depending on where they need to go next. Redman and her team believe that Golgi or Golgi-like bodies transport materials within the cell to form sheets around vesicles, like those seen in S. favosa. The hypothetical Golgi bodies themselves are not thought to have contained these lamellae.

This type of complex sorting of cellular contents is a feature of all modern eukaryotes. “Including varieties Satka Favosa… are considered [eukaryotes] They have a complex vesicle structure, the researchers said in the study Stady. These new fossils indicate that they originated very early in their history.

Clearly, eukaryotes have been more complex and diverse than we thought for hundreds of millions of years longer than we thought. There may be older specimens out there. While fossil evidence for eukaryotes from somewhere close to their origin eludes us, specimens more than a billion years old, like the one found by Redman and her team, tell us more than ever about their evolution, and thus ours.

Papers in Paleontology, 2023. DOI: 10.1002/spp2.1538