FunNature & AnimalThe mysterious fauna of Edicara

The mysterious fauna of Edicara

In 1947 Reginald Sprigg was the geologist on an expedition searching for copper in Ediacara , an arid, reddish area of southern Australia near Adelaide and adjacent to the Flinders Mountains. But his passion was fossils, so whenever he had free time he spent time looking for fossils.

And what he found were the remains of strange life forms that swarmed the ocean floor 600 million years ago. It took Sprigg two years to convince the skeptical paleontological community of the importance of his discovery. And it was not for less, because he was showing them a totally new and strange world: they were soft-bodied beings, without a skeleton or other hard parts -such as shells- . Their traces have been found from Canada and Arctic Siberia to Newfoundland or Nabimia.

With an absolutely strange appearance, its place in the tree of life is one of the great unsolved mysteries of paleobiology . So much so that, for example, the same fossil has been classified by paleontologists as an algae, a lichen, a giant protozoan or a natural rock formation unrelated to a living being.

One of the places where we find the best examples of the Ediacaran biota is in the Nama plains, in Namibia. They were discovered in 1908, and between 1929 and 1933 the many specimens he discovered there were described in great detail by the German paleontologist Georg Gürich . But the paleontological community didn’t know what to do with them. How is it possible?

We must bear in mind that, with very rare exceptions, the fossilization process leaves no trace of the anatomy or physiology of animals . From the dinosaurs we are left with the bones (and very rarely traces of skin) and from them we can deduce something of their biology because we can relate their ribs, spine and teeth to living animals. The same thing happens with trilobites, the fossil-star of the following period, the Cambrian: although their segmented body and articulated legs became extinct millions of years ago, we find them in today’s arthropods. And this is where the problem with the Edicara fossils lies: there is no way to relate their structure to anything known.

The Nama plains are dotted with hills that resemble burial mounds from past civilizations. They were actually built by tiny cyanobacteria when they were a shallow seafloor, during the Ediacaran period , 543 million years ago.

The world then was truly strange . The oceans contained so little oxygen that modern fish would not last long in those waters. The seabed was covered by a sticky carpet of photosynthetic bacteria on which lived enigmatic beings whose bodies some looked like thin, padded pillows similar to jellyfish , others tubular , and others more like fern leaves . None had a recognizable stomach or digestive system, and they lived in shallow , well-lit water, so it is thought that they could photosynthesize . In fact it is possible that they had photosynthetic algae in their tissues or that they fed through their “skin”. Most remained motionless, but a few were able to wander blindly. Among all of them , one of the most mysterious is a segmented, wide and oval being, Dickinsonia . Fossils have been collected in their different stages of growth (some specimens up to a meter in length) but no indication of their internal structure has been found. Moreover, it is not known at which of the two extremes his head was… if he had one. Be that as it may, the life of these Vendozoans -which is how the Edicara fauna is known- was calm: there were no predators and they did not have to fight for food.

More than 30 genera have been identified, and although more than 70 years have passed since Sprigg’s discovery, we still don’t know what they were: the oldest ancestors of modern animals, such as sponges, pennatulaceans (a form of soft coral) or segmented worms , or on the contrary they are the relics of a failed evolutionary experiment, completely unrelated to current organisms. In other words, they are like living beings from another planet, relics of times long forgotten.

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