Fossils

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Classically, the science that studies the evolutionary history of species is paleontology. So what can it teach us about the ancient history of eukaryotes?

The appearance of the first animal fossils dates at the separation between the Precambrian and the Cambrian around 544 Ma (= million years) ago. Previously, i.e. during the Proterozoic era (2,500 Ma to 544 Ma ago), there is a fossilized microbial fauna which contains prokaryotic cells but probably also eukaryotes. Indeed, there are fossils resembling perfectly preserved red bangiophyte algae, and possessing all the characteristics of these, such as multicellularity and sexual reproduction, dating back to 1,200 Ma (see Figure 216). Before, fossils are more difficult to interpret. In sediments dating to around 1,800 Ma ago, one can find cells which resemble cysts or thecae of certain flagellates and certain amoebae (achritarchs). Likewise, “algae” of the genus Grypania are present in rocks dating back to 2,100 Ma ago. The size of these fossils and their complexity suggest that they may have come from eukaryotes. Before, during the so-called Archean era (before 2,500 Ma ago), there are no fossils.

In conclusion, the fossils suggest that eukaryotes may have a very ancient origin dating back more than two billion years.

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