Researchers learn more about first fossil’s evolutionary history

Researchers in UC Riverside’s Department of Earth Sciences have uncovered more about the enigmatic fossil Dickinsonia. UCR Professor of Paleontology Mary Droser and graduate student of the Department of Earth Sciences Scott Evans co-published a study on the growth and development of this animal and its attributes.

Dickinsonia is the oldest animal found in the Ediacaran period which occurred approximately 600 million years ago. Determining the taxonomic rank has been a difficult case for researchers, especially since little information is known about its history. Since the fossil’s discovery, it has been established that it is an extinct animal with its own clade, or group, in the phylogenetic lineage of animals, placed between sponges and the last common ancestor of protosomes and deuterosomes.

The discovery of this fossil was made by a cattle rancher in South Australia in the 1940s. This discovery was noteworthy in the fact that this particular location, known as Flinders Ranges, holds the most abundant community of fossilized soft-bodied organisms in any part of the world. These soft-bodied organisms include Dickinsonia, a flat-bodied soft animal that swam in shallow waters and fed on algae.

Droser surmised, “these are the oldest animals … there’s reason to suggest that they’re animals but Dickinsonia in particular has been interpreted as a worm, a Placozoan, as a fungi … as a bilaterian, so it has a lot of interpretation. So one of the questions (could be) how does it fit on an animal tree and is it an animal?”

Further research went into understanding the growth, morphology and classification of this animal where several discoveries were made. For one, the animal lacks a digestive tract and rather feeds on algae through its underside, crossing off the possibility of it being a bilaterian, despite its bilaterally symmetrical appearance.

In addition to that, the structure of the animal’s physiology allowed researchers to understand the way it grows and develop. Droser remarked that Dickinsonia grew in a “highly regulated manner as it added its modules in a very systematic way in order to keep an oval shape. It basically maximized its surface area and maintain(ed) its length-to-width ratio and that highly regulated growth was really surprising. Being that it’s earth’s first animal, it’s not expected for a specimen like this to be so regulated.” These modules, grown through terminal addition, served to help the Dickinsonia with feeding, mobility and having a proportional body size.

From these new conclusions, Droser and her team hope to find more information about Dickinsonia and how life may have been life in the past.


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