At the edge of a desert in southern Namibia, scientists have found the remains of the oldest known animal reef system in the world.

The reef was constructed 548 million years ago in what was once a shallow sea. Prior to its discovery, the oldest known reef system constructed by animals was 530 million years old.

If you could snorkel over this ancient reef all those millenniums ago, you would find a vast system that stretched for more than four miles.

Most of it would be covered by mounds of green slime created by microbes that had been constructing primitive limestone reefs for 3 billion years.

But every once in a while you would come across a more sophisticated structure — a small thicket of cornucopia-shaped shells that look like a stack of ice cream cones fitted into one another. The hard structures were attached to one another by a cement-like material.

This early reef system was built by an animal species known as Cloudina, which is the first animal known to have a hard shell, said Amelia Penny, a Ph.D. student at the University of Edinburgh’s School of Geosciences. Penny was the lead author of a paper describing the reef’s discovery published Thursday in the journal Science.

Cloudina were a filter-feeding animal, but nobody knows exactly what they looked like because fossilized remains of their soft tissue have never been found. Prior to this study, scientists also didn’t know how they spent their lives — whether they laid around on the seafloor or if they attached themselves to rocks.

"We found them in life position, forming a reef," said Penny. "So this study reveals at least one of the ways in which they definitely grew."

The researchers also noted that some of the Cloudina shells appear to have a little drill hole in them, suggesting there were creatures that were preying on these small animals. That in turn implies that the ecology of this time, more than 5 million years before the Cambrian explosion when life went through a rapid diversification, was more complex than previously thought.

"This reef dates back to a pivotal piece of time when life is just starting to get complicated and complex," said Rachel Wood, a professor of geosciences at the University of Edinburgh, who worked with Penny on the study. "It is the very beginning hint of the modern world."

Wood and Penny said they were interested to learn more about the evolutionary pressures that drove these animals to build shells for themselves and then to congregate in reefs on the seafloor.

"We are only just starting to delve into this subject and get to grips with the complexity we suspect is there," said Wood.