The Cambrian Period is famous for the explosive emergence of animal groups in a short period of time. Less well-known to the public is the earlier Ediacaran Period, home to some of the earliest organisms visible to the naked eye. They come in a variety of shapes and sizes, but many are flat and appear to be made of repeated units, looking like weird air-mattresses or quilts.
Just what those Ediacaran organisms are related to has been the focus of much debate since their discovery. Possible relationships included representing living animal groups, lichens, fungi, a completely extinct multicellular kingdom, or gigantic single-celled organisms. Paleontologists Renee Hoekzema and colleagues have conducted research showing that at least one of these strange organisms, Dickinsonia, is an animal.
Dickinsonia is one of the largest and most iconic Ediacaran organisms, being roughly oval-shaped with the largest specimens nearly 1.5 meters (5 feet) long, but only a few centimeters thick. Its body is made up of numerous inflated segments or “units” reflected across the central axis, and one large, wedge-shaped segment at the blunt end, called the “deltoidal region.” The smallest and presumably youngest specimens of Dickinsonia have proportionally larger deltoidal regions and fewer units, while the largest specimens have smaller deltoidal regions and many more units.