The Storm That Made a Fossil of a Continent: South Australia's Ediacara Hills

In the Flinders Ranges of South Australia, a low ridge of quartzite and sandstone holds the imprint of a world before skeletons. The hills are unremarkable—arid, scrub-covered, the kind of place a traveller might pass without slowing—but the fossils they contain are anything but. Here, in a 560-million-year-old seafloor, Earth's first complex multicellular organisms were buried alive by storm-driven sand, pressed into the rock as casts and moulds of bodies that had no bones, no shells, no hard parts at all.

The Garden in the Sand

The Ediacara Hills sit within a 650-kilometre belt of sedimentary rock known as the Flinders Ranges, laid down between 600 and 500 million years ago. At that time, the landmass that would become Australia was part of the supercontinent Rodinia, drifting near the equator. Shallow seas covered much of the region, their muddy bottoms occasionally swept by storm surges.

In 1946, geologist Reg Sprigg was mapping the area for the South Australian Department of Mines when he noticed strange, disc-shaped impressions on slabs of weathered sandstone. They looked like jellyfish, but jellyfish don't fossilise well. Sprigg had stumbled upon something older and stranger: a whole community of soft-bodied organisms preserved in sand, a fossil assemblage unlike anything then known.

It took years for the scientific community to accept what Sprigg had found. The Ediacaran biota—named after the hills—represents the first widespread radiation of complex, multicellular life on Earth, predating the Cambrian explosion by roughly 40 million years.

Bodies Without Bones

The Ediacaran organisms were unlike anything alive today. Some were frond-like, anchored to the seafloor by a holdfast, standing upright in the current like underwater ferns. Others were disc-shaped, perhaps floating or lying flat on the sediment. Dickinsonia, one of the most famous genera, resembled a ribbed oval mattress up to a metre long, and may have absorbed nutrients directly through its skin.

No Ediacaran organism had a mouth, a gut, or any means of moving. They were filter-feeders, grazers of microbial mats, or osmotrophs—creatures that fed by absorbing dissolved organic matter from seawater.

The preservation is exceptional because it is entirely mouldic. A storm surge buried the organisms in a pulse of sand; the sand hardened into sandstone while the organic bodies decayed, leaving hollow impressions. Later, finer sediment filled those hollows, creating natural casts. Today, splitting a slab of Ediacaran sandstone can reveal both the negative impression of the organism's upper surface and the positive cast of its underside—a three-dimensional record of a body plan that has no modern counterpart.

A World Before Predation

What makes the Ediacaran biota so strange is not just their shape but their ecology. These were gentle worlds. No Ediacaran fossil shows evidence of predation: no bite marks, no healed wounds, no shells evolved for protection. The seafloor was a placid garden of fronds, discs, and quilted mats, where organisms grew slowly and died of old age or burial.

That changed with the Cambrian explosion, when animals evolved skeletons, jaws, and the ability to move. The Ediacaran body plans—soft, sessile, defenceless—were ill-suited to a world with predators. Almost all of them vanished, replaced by the ancestors of modern animal phyla. The Ediacara Hills preserve a last glimpse of that vanished Eden, frozen in sandstone moments before the storm.

The Site Today

The Ediacara Hills fossil site is now part of the Nilpena Ediacara National Park, established in 2021 to protect the most significant fossil beds. Researchers have identified more than 50 species from the formation, some so unusual they have been placed in their own biological kingdom. The fossils remain remarkably fresh: the same storm surge that buried the organisms also sealed them from oxygen, preventing decay and preserving details as fine as the ribbing on a Dickinsonia or the branching pattern of a Charniodiscus frond.

Walk the ridge today and you can still find slabs of sandstone bearing the ghostly discs and fronds of those ancient forms. They lie exposed to the sun, weathering slowly back into sand, 560 million years after the storm that made them permanent.