Dickinsonia

Dickinsonia is a genus of extinct organism that lived during the late Ediacaran period in what is now Australia, China, Russia, and Ukraine. It had a round, approximately bilaterally symmetric body with multiple segments running along it. It could range from a few millimeters to over a meter in length, and likely lived in shallow waters, feeding on the microbial mats that dominated the seascape at the time.

As a member of the Ediacaran biota, its relationships to other organisms has been heavily debated. It was initially proposed to be a jellyfish, and over the years has been claimed to be a land-dwelling lichen, a placozoan, or even a giant protist. Currently, the most popular interpretation is that it was a seafloor-dwelling animal, perhaps a primitive stem group bilaterian, although this is still contentious. Among other Ediacaran organisms, it shares a close resemblance to other segmented forms like Vendia, Yorgia, and Spriggina, and has been proposed to be a member of the phylum Proarticulata or alternatively the morphogroup Dickinsoniomorpha. It is disputed whether the segments of Dickinsonia are bilaterally symmetric across the midline, or are offset from each other via glide reflection, or possibly both.

Description

Dickinsonia fossils are known only from imprints and casts in sandstone. These fossils can range from just a few millimeters to about 1.4 meters (4 feet 7 inches) in length. They have a nearly symmetrical, segmented body that is round or oval shaped, slightly wider at one end. The segments are arranged in a special way, and scientists debate how exactly they were positioned on the organism.

The body of Dickinsonia is thought to have been sack-like, with a tough outer layer. Some fossils show internal structures, and it is suggested that Dickinsonia grew by adding new segments at one end. It likely did not stop growing and could repair itself if damaged.

Ecology

Dickinsonia was likely a creature that moved along the ocean floor. It probably ate special layers of tiny life on the sea bottom using parts on its underside. Scientists have found marks in the sand that look like Dickinsonia, showing how it may have fed. A study from 2022 thinks Dickinsonia might have stuck to the sand using a slimy substance, helping it live in very shallow water.

Taphonomy

Fossils of Dickinsonia are found as imprints on the bottom of sandstone layers. These imprints show the top sides of the creatures that were buried by sand. The sand hardened before the creatures fully broke down, preserving the shapes. Sometimes, these imprints are squished or stretched.

Very rarely, Dickinsonia fossils are found as solid shapes in big sandstone chunks. These are often found together with other ancient creatures like Pteridinium, Rangea, and others. Large groups of Dickinsonia fossils are preserved in Nilpena Ediacara National Park, where park rangers lead tours during cooler months. These fossils show what happened when creatures were moved from the sea floor by sand flows, sometimes stretching or tearing their shapes. One of these unusual fossils was once thought to be a different type of creature but was later identified as Dickinsonia.

Taxonomy

History

Dickinsonia was first found in 1946 in the Flinders Ranges in South Australia. It was named after Ben Dickinson, who was the Director of Mines for South Australia at the time. More examples of Dickinsonia have been discovered in Ukraine, Russia, and China.

At first, scientists thought Dickinsonia might have been a jellyfish-like creature from very early times. Over the years, many ideas about what Dickinsonia was have been suggested. Some thought it might be related to animals with segmented bodies, while others proposed different groups. Recently, some scientists have suggested it might have been an early animal, but its exact place in the tree of life is still uncertain.

Modern classification

Today, many scientists believe Dickinsonia might have been an early relative of animals, but its exact classification is still debated. Some studies have found a substance called cholesterol in Russian specimens, which is usually made by animals, but this is still being discussed. Dickinsonia had clear left and right sides, suggesting it had a simple body plan, but it did not have a mouth or gut like most animals today.

Species

Since 1947, scientists have described 11 species of Dickinsonia. Currently, three are considered valid, two are still being studied, and the other six are no longer considered correct.