More than 540 million years ago, a mass extinction took place on our planet wiping out soft-bodied organisms. What caused the world’s first mass extinction, known as the end-Ediacaran extinction, is debated amongst experts. Now, based on fossils from Namibia, Vanderbilt University researchers have a new theory: it was caused by newly evolved biological animals.

The earliest microbes, Ediacarans, were on Earth for over 3 billion years when multicellular organisms came into existence by discovering how to catch and harness the energy in sunlight. Researchers have pieced together that Ediacarans critters were “largely immobile form of marine life shaped like discs and tubes, fronds and quilted mattresses.” Sixty million years later, towards the end of the Ediacaran period and the start of the Cambrian era, the first animals (called metazoans) came to be.

"These new species were 'ecological engineers' who changed the environment in ways that made it more and more difficult for the Ediacarans to survive," said Simon Darroch, assistant professor of earth and environmental sciences at Vanderbilt University, in a statement.

The newly discovered remnants—located in the Zaris subbasin in the southwest African nation—contained the preserved Ediacara biota, metazoan body fossils, and metazoan trace fossils. According to the researchers, who published their findings in the journal Palaeogeography, Palaeoclimatology, Palaeoecology, the fossils show an ecological connection between Ediacarans and animals, as some of them show Cambrian critters wrapped around Ediacarans.

“Until this, the evidence for an overlapping ecological association between metazoans and soft-bodied Ediacaran organisms was limited,” said Darroch. “Here, we describe new fossil localities from southern Namibia that preserve soft-bodied Ediacara biota, enigmatic tubular organisms thought to represent metazoans and vertically oriented metazoan trace fossils. Although the precise identity of the tracemakers remains elusive, the structures bear several striking similarities with a cone-shaped organism called Conichnus that has been found in the Cambrian period.”

Thus far, the challenge in connecting the dots has been the lack of fossils. Since the early microbes did not have shells or skeletons, not much is preserved aside from trace impressions.

“We don’t know very much about the Ediacarans because they did not produce shells or skeletons. As a result, almost all we know about them comes from imprints of their shapes preserved in sand or ash,” said Simon Darroch, assistant professor of earth and environmental sciences at Vanderbilt University, in a previous statement.

There have been five mass extinctions in the history of the planet, known to date, and some scientists believe that we are on the brink of the sixth. Should this be true, Darroch knows the animal responsible.

“There is a powerful analogy between the Earth’s first mass extinction and what is happening today,” said Darroch. “The end-Ediacaran extinction shows that the evolution of new behaviors can fundamentally change the entire planet, and today we humans are the most powerful ‘ecosystems engineers’ ever known.”