Tiny microscopic creatures created a reef 548 million years ago, and this ancient structure is the oldest-known feature of its kind in the world. Constructions like these are similar to modern coral reefs. However, this structure is 18 million years older than any other in the world. It is found in Namibia, and is now located on dry ground.

Cloudina, the animals that created this feature look like stacked ice cream cones. The miniscule creatures were filter-feeders and were the first known life form to possess hard shells. Researchers speculate that the ancient animals were first developing the ability to form shells and create reefs. Evolution favored both traits because of harsh environmental conditions on Earth at that time.

Discovery of this reef revealed important changes were happening in lifeforms millions of years before the Cambrian explosion 542 million years ago. Most major forms and body shapes of animals burst into existence during a period of 10 million years. Archeologists believe that before the rapid burst in the number of species, all animals had soft bodies. Development of biomineralisation - the ability to create rigid structures - led to a great increase in the biodiversity of the oceans.

The Ediacaran Period, during which Cloudina lived, was a highly-unusual period in the history of life on Earth. Before that time, life consisted largely of bacteria and green algae. Large life forms suddenly become prevalent at this point in the fossil record, the so-called Ediacara biota. These were the first animals in the waters of the planet.

Natural reefs are created through sedementation of rock and erosion. Cloudina secreted a cement-like substance, rich in calcium carbonate, that could bind the creatures together. They latched on to one another in ancient seas, long since vanished.

"We have found that animals were building reefs even before the evolution of complex animal life, suggesting that there must have been selective pressures in the Precambrian Period that we have yet to understand," Rachel Wood of the University of Edinburgh, said.

Previous studies suggested environmental pressures could have driven the great rise in the number of species in the Cambrian Explosion. This new research on an ancient reef could lend evidence to the theory.

Predators, roaming the seas for the first time in the history of the planet, could have provided an environmental pressure driving construction of the reef. The structures might have also allowed the life forms access to nutrient-rich waters, as competition for sustenance was becoming more common.

Study of the ancient reef and evolutionary pressures on one the world's earliest animals was published in the journal Science.

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