Dickinsonia is an Ediacaran organism, possibly a bilateral animal and ancestor of chordates, with scroll symmetry. It left footprints and lived 560-541 million years ago. Its classification is unknown and it disappeared with the rest of the Ediacaran fauna at the dawn of the Cambrian.
Dickinsonia is an iconic organism of the Ediacaran fauna, which is among the earliest known representatives of multicellular life on the planet. Dickinsonia appears as a ribbed oval with scroll symmetry. It remained stationary for most of its life, although it may have moved from resting place to resting place at times. Like other Ediacaran organisms, there is much debate about Dickinsonia’s affinity, although most workers believe it is a bilateral animal, possibly an ancestor of chordates. However, its realm-level classification is officially incertae sedis (unknown classification).
Dickinsonia lived about 560 – 541 million years ago, during the Late Ediacaran. It was contemporary with other strange Ediacaran organisms, which resemble sacks, stalks and mattresses filled with mud. These are not animals as we know them. Dickinsonia is sometimes placed in the phylum Proarticulata, which would be the only animal phylum to become completely extinct if it actually existed. Other animals sometimes included in this phylum are Yorgia, Vendia, Archaeaspinus, Andiva and Ovatoscutum. These animals were not truly bilateral, but did possess bilateral “sliding reflection” symmetry, in which one side was partially misaligned with the other.
Dickinsonia left unskeletonized footprints that have been found in the famous Flinders Ranges of South Australia, as well as Rajastan in India, Podolia in Ukraine and the White Sea region of Russia. The fossils range wildly in size from 4mm (tiny) to 1.4m (human size). This extreme variation has prompted some paleontologists to consider Dickinsonia a fungus or protist rather than an animal, but there are other examples in the animal world of this variation. Dickinsonia evidently continued to grow on all scales until it was covered in sediment or otherwise killed.
Dickinsonia disappeared along with the rest of the Ediacaran fauna at the dawn of the Cambrian. The reason for this extinction is unknown, but hypotheses include the usual suspects (volcanism, asteroid impact, etc.) but also some new ones, including the advent of predators or being overtaken by more effective Cambrian organisms. Without more fossil and paleoclimatic evidence, we may never know.
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