Dickinsonia

Dickinsonia is one of the most iconic and enigmatic organisms of the Ediacaran Biota, a collection of the earliest known complex, multicellular life forms. First discovered in the Ediacara Hills of South Australia, these fossils appear as flat, bilaterally symmetrical, oval-shaped impressions in sandstone beds. Their bodies were composed of numerous rib-like segments, or isomers, that radiated from a central groove or ridge. These segments exhibit a distinctive pattern of 'glide reflection' symmetry, where segments on one side are offset from those on the other, a feature not seen in modern animals. Dickinsonia could range in size from a few millimeters to over a meter in length, making it one of the largest Ediacaran organisms. For decades, its classification was hotly debated, with proposals ranging from fungi and lichens to a failed evolutionary experiment. However, the 2018 discovery of preserved cholesterol molecules—a fat biomarker characteristic of animals—in a Dickinsonia fossil from Russia provided strong evidence that it was indeed an early animal. It is believed to have been a mobile benthic organism, crawling along the seafloor and absorbing nutrients from the microbial mats below through its underside, a feeding method known as osmotrophy. Dickinsonia's significance lies in its status as a potential stem-group animal, offering a crucial glimpse into the very dawn of animal life before the Cambrian Explosion, a period when most major animal body plans appeared.