Hundreds of disc-shaped fossils of varying sizes were found in sandstone sediment in the Cerro Negro Formation of Argentina. They show what scientists believe are among the oldest living forms from the Ediacaran Period, around 569 million years ago.
Discovered in 2015 by Brazilian and Argentine researchers, the disc- and egg-shaped remains are large, with a diameter ranging from 6 to 16 cm (2.3 to 6.9 in). Some of them are distinctively ornate, showing radial grooves. The fossils correspond to the genus Aspidella, likely the imprint of a stalked animal’s attachment to an anchoring substrate. This is the first time that these fossils were found in this region.
First described in the 19th century, Aspidella is among the most abundant of the Ediacaran biota, comprising mostly sessile marine organisms with simple bodies that represented the first wide variety of macroscopic life-forms on Earth. Before these organisms arose, the seas of the planet were inhabited only by single-celled organisms such as bacteria, or simple colonies.