On a quiet mudflat in northern Australia, the sun has just set and the moon rises quietly in the distant sky. Hidden in this ancient mud are traces of our ancient ancestors – a diverse and complex group of tiny life forms.
Researchers from the University of California, Santa Barbara and McGill University reveal in a report on beautifully preserved microfossils that even 1.64 billion years ago, eukaryotes had evolved into many different forms. The study, published in the journal Papers in Paleontology, documents an assemblage of eukaryotic fossils from this period and describes four new species types, as well as some of the advanced features that had emerged in these early eukaryotes.
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The fossils revealed an astonishing diversity and complexity, recording 26 taxa, including 10 previously undescribed species. The team found indirect evidence that these organisms possessed a cytoskeleton, as well as some plate-like structures that hinted at the presence of “internal vesicles” – possibly the ancestors of the Golgi apparatus in modern eukaryotic cells. The cell walls of some other microorganisms are composed of bound fibers, which also implies the existence of a complex “cytoskeleton.”
The researchers also found cells with tiny trap doors, suggesting a degree of specialization. Some microorganisms can form cyst-like structures to protect against adverse environmental conditions. In order to appear, they need to be able to make an opening in their protective shell. Making this door is a specialized process.
Part of this research explores the evolution of early eukaryotes. Riedman and Porter wanted to understand the environments in which early eukaryotes diversified, why they were there, when they migrated elsewhere, and the adaptations required to adapt to new ecological niches.
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having mitochondria
Limbunyasphaera operculata is a new species characterized by a small doorway in its cells. (Photo/Riedman)
A large part of this work involves understanding when different features of eukaryotes first appeared. For example, the authors are very interested in whether these organisms have adapted to oxygen-rich or oxygen-poor environments. The former would suggest that they have aerobic metabolism and may possess mitochondria. Every modern eukaryote that has been discovered descends from an ancestor that had mitochondria. This suggests that eukaryotes acquired this organelle very early and that it provided significant advantages.
Riedman and Porter are currently working on a new report on changes in eukaryotic diversity over time. Meanwhile, their geochemist collaborators are leading a study at McGill University on oxygen levels and the eukaryotes’ preferred habitats, aspects that may shed light on their evolution.
“These results are an instruction to look for older material, older eukaryotes, because this is clearly not the beginning of eukaryotes on Earth,” Riedman said.
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Source of first picture: DALL.E
Image source: Riedman et al.cc By4.0
Reference papers:
1.Early eukaryotic microfossils of the late Palaeoproterozoic Limbunya Group, Birrindudu Basin, northern Australia.Papers in Palaeontology
Further reading:
1.“I want to be a good person” makes bad cells good: using phagocytosis to fight cancer
