Dickinsonia, the oldest confirmed animal

Dickinsonia is a flat, oval organism marked with dozens of parallel ribs, found in rocks from about 571 to 541 million years ago. The first specimens came from the Ediacara Hills of South Australia, where geologist Reg Sprigg collected them in 1946; they were named for Ben Dickinson, the state's Director of Mines. The largest reach about 1.4 metres in length, yet they were only a few millimetres thick, like a rubber mat on the seafloor.²³

For decades nobody could say what it was. Adolf Seilacher suggested it belonged to a separate, failed experiment he called Vendozoa, others thought it was a lichen, a fungus or a giant single-celled organism. In 2018 Ilya Bobrovskiy, Jochen Brocks and colleagues settled much of the question. They extracted molecules from exceptionally preserved Dickinsonia from the White Sea coast of Russia, about 558 million years old, and found cholesterol, a fat made by animals. Plants, fungi and most protists make other sterols, so the finding places Dickinsonia in the animal kingdom, making it the oldest animal that can be confirmed from chemistry.¹²³

Resting traces preserved in rock show that Dickinsonia could shift position over microbial mats on the seafloor. It probably fed by absorbing nutrients from the mat beneath its underside, without a mouth, and its body plan has no obvious modern equivalent. It belongs to the Ediacaran biota that spread across the ocean floor before the Cambrian, and its exact place on the animal family tree, and whether it left descendants, remains unknown.¹³