Evolution: Fossils of Ancient Flat Sea Animals Shed Light on Why Animals Are Bilateral
Earth's early life came from the planet's oceans, as laid out in current evolution theories. Among them would be a class of broad, flat marine animals called Dickinsonia, which lived more than 550 million years ago.
Dickinsonia is part of a group of marine life fossils called the Ediacaran Biota, and this group could be the oldest fossil evidence currently discovered that shows the physical forms of animals, according to the PLOS journal. The evidence left behind for evolution scientists are abundant enough, especially in South Australia where most of the studies on Dickinsonia were conducted.
From the hundreds of fossils found of the flat animals, scientists now have an idea of the evolutionary transition made from sponges to bilaterians, a diverse group of animals characterized by a symmetric form.
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Modern animals, as well as humans, are considered bilaterians. Bilaterians are beings which have two similar sides when their bodies are divided by a straight line in the middle.
As the most numerous and earliest example of bilaterians preserved in fossil records, Dickinsonia has been thoroughly studied by scientists. From these extensive research studies, they inferred that the early animals had soft bodies, which were oval shaped, flat, and bilaterally symmetrical. Their bodies could also have been covered in raised ridges or layers called modules.
As what is evident on the cluster of Dickinsonia fossils, the proto-animals also displayed a tendency to form colonies. Researcher Scott Evans said in a statement to the University of California that "Dickinsonia most likely represents a separate group of animals that is now extinct, but can tell us a lot about the evolutionary history of animals."
Particularly interesting for his team is how the large prehistoric animals, who could grow as large as several feet wide according to their imprints, were able to move around and organize. Dickinsonia, according to Evans, were the first sea animals that were able to "become large and complex, to move around, and form communities," the researcher noted.
