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The Ediacaran biota are a mysterious type of life found in the fossil record prior to the Cambrian era, which began about 542 million years ago. They were the first multicellular life forms which left fossils. Paleontologists do not even completely agree on whether or not the Ediacaran biota can even be categorized using the current biological classification scheme.
Emerging about 610 million years ago, the Ediacaran biota had largely disappeared by the beginning of the Cambrian era. Based on how alien they are to modern life, some paleontologists believe the Ediacaran biota were a "failed experiment" which died out, and that the biodiversity which later emerged from the Cambrian was based on another evolutionary trajectory from single-celled organisms. About 100 different Ediacaran species have been described, with roughly 10 surviving past the period.
The period known as the Ediacaran began 630 million years ago, immediately after the 220 million-year-long Cryogenian Period, which was characterized by two of the worse glaciations in planetary history, which some paleontologists believe completely covered in the Earth in ice. Very shortly after the ice receded, the first embryo-like fossils appear, although some think these are merely the fossils of very large bacteria. If the embryos are real, then multicellular life may have appeared only a few million years after temperate weather returned to Earth.
The Ediacaran biota include the mollusk-like Kimberella, which was originally thought to be a box jellyfish; the extremely simplistic bulb-like Vernanimalcula, one of the earliest ancestors of all bilateral animals; the disc-like Ediacaria, which could have been plant, animal, or fungi; the bag-shaped Pteridinium, which lacks practically all features traditionally associated with multicellular life; Dickinsonia, an ovoid, ridged worm; and Cyclomedusa, the most numerous Ediacaran fossil, a bottom-dwelling polyp.
As the first actual animals, the Ediacaran biota are of great interest to evolutionary biologists. Some of the strata in which they are found are remarkably well-preserved. They allow the analysis not just of many species, but their developmental stages from larvae to adolescent to adult.