In 1946, a young Australian geologist named Reginald Sprigg was eating his lunch in the dry, rugged hills of the Flinders Ranges in South Australia, idly turning over slabs of ancient rock, when he noticed something on their surfaces.
Impressions. Strange, faint, leaf-like shapes pressed into the stone. They looked like the fossils of soft-bodied creatures — but they were in rock far, far older than anything that was supposed to contain complex life.
Sprigg had stumbled onto one of the most important fossil discoveries of the twentieth century. The hills he was sitting in would give their name to an entire chapter of Earth’s history: the Ediacaran Period. And the creatures pressed into those rocks would turn out to be among the strangest things that have ever lived.
A world before the world we know
To understand why the Ediacaran biota matter, you have to understand what came after them.
Around 540 million years ago, the planet underwent what scientists call the Cambrian explosion — a relatively sudden burst of evolutionary creativity in which almost all the major animal body plans we know today appeared. Eyes, shells, legs, jaws, backbones-to-be. The ancestors of nearly every living animal group trace back to that explosive window.
The Ediacaran biota lived before that. The Flinders Ranges fossils date to roughly 550 million years ago — in the stretch of time immediately preceding the Cambrian, when complex multicellular life was, for the first time anywhere, getting large enough to see.
Before the Ediacaran, life on Earth was almost entirely microscopic. Single cells. Bacterial mats. For billions of years, nothing more. The Ediacaran organisms were the first wave of life big enough to leave a clear body impression in the sand — the moment the planet went, in evolutionary terms, from tiny to tremendous.
And what that first wave looked like is genuinely difficult to imagine.
Creatures unlike anything alive
The Flinders Ranges have produced more than a hundred described genera of these organisms, and many of them resist comparison to anything alive today.
There were frond-like forms — creatures shaped like leaves or feathers, anchored to the seafloor, some of them branching in intricate, repeating, fractal-like patterns. There were flat, segmented, oval organisms that looked like quilted air mattresses. There were discs, ribbons, and shapes that look, to a modern eye, more like abstract art than biology.
The most famous is Dickinsonia — a flat, ribbed, oval creature that could grow well over a metre long. And Dickinsonia is the organism that captures what’s so strange about this whole world. Recent chemical analysis of its fossils has confirmed it was an animal. But it was an animal with no eyes, no mouth, and no gut. It appears to have fed by simply absorbing nutrients directly through the underside of its body, settling onto the microbial mats that carpeted the Ediacaran seafloor and digesting them externally, then moving on.
An animal that ate by lying on its food. No mouth required.
It’s this quality — recognisably alive, clearly complex, and yet built on principles that no surviving animal uses — that has made the Ediacaran biota one of the great puzzles of palaeontology.
So what were they?
Here is where the science gets genuinely unsettled, and genuinely interesting.
For decades, one influential interpretation held that the Ediacaran biota were an evolutionary dead end — a “failed experiment.” In this view, championed by the palaeontologist Adolf Seilacher, these organisms were not the ancestors of anything. They were a first, separate attempt at large complex life, built on a body plan that didn’t survive, wiped out or outcompeted before the Cambrian and replaced by the lineages that led to modern animals. A discarded first draft.
It’s a haunting idea — a whole world of complex creatures that simply ended, leaving no descendants. And for the strangest of the Ediacarans, the frondy, mouthless, gutless forms with no clear modern relatives, it may well be true.
But the picture has become more complicated, and the “failed experiment” framing is no longer the consensus.
Because not all the Ediacarans were dead ends. The Flinders Ranges beds also preserve a creature called Kimberella — and the same kind of chemical analysis that revealed Dickinsonia’s strangeness revealed something different about Kimberella. It had a mouth. It had a gut. It digested food much the way modern animals do. Kimberella is now widely interpreted as an early bilaterian, possibly related to the ancestors of molluscs — a recognisable forerunner of later animal life.
Other Ediacaran forms have been identified as early cnidarians — the group that today includes jellyfish and corals. So the honest answer to “what were they?” is no longer a single answer. Some of the Ediacaran biota appear to have been genuine evolutionary dead ends. Others look like genuine ancestors. They were a mixed assemblage — part discarded experiment, part the actual root of the animal kingdom.
Why the mystery is the point
It would be neater if the Ediacaran story had a clean ending. Either “these were our ancestors” or “these were evolution’s abandoned first try.” The truth, as best science can currently tell, is both at once — and that is what makes the Flinders Ranges fossils so scientifically valuable.
They capture a genuine threshold. The moment, 550 million years ago, when life first became big and complex — and when evolution was, in effect, trying several different answers to the question of how to build a large organism at the same time. Some of those answers worked and led to everything that followed, including us. Some of them simply ended, leaving nothing behind but impressions in South Australian sandstone.
The Flinders Ranges preserve that experiment in progress. It is one of the only places on Earth where you can stand in the open air and look at the rock record of the very first chapter of complex life — a chapter written before the Cambrian, before shells, before eyes, before almost everything.
Reginald Sprigg, eating his lunch in 1946, had no idea he was looking at the dawn of animal life. It took decades for science to even begin to understand what he’d found.
In some important ways, it still hasn’t finished. The frond-like creatures pressed into those ancient rocks are still, more than five hundred million years after they lived, keeping most of their secrets.
