A stone slab barely half a meter wide is shaking the foundations of evolutionary science.

Embedded in the slab’s fine sandstone are delicate imprints: long toes ending in sharp claws, left by an animal that trotted through mud 355 million years ago. According to a study out today, these are the oldest known footprints of an amniote — the group that includes reptiles, birds, and mammals.

“I’m stunned,” said Per Ahlberg, a paleontologist at Uppsala University and the study’s lead author. “A single track-bearing slab, which one person can lift, calls into question everything we thought we knew about when modern tetrapods evolved.”

Rewriting the Tetrapod Family Tree

The story of how the first land vertebrates appeared is thought to have unfolded in two distinct acts. First came the Devonian Period. Fishlike “tetrapods” with rudimentary limbs began flopping through marshes. Then, in the Carboniferous Period that followed, fully terrestrial creatures like amphibians and reptiles began to diversify. These would eventually give rise to dinosaurs, birds, and mammals.

But the new discovery suggests that those two acts overlapped at some point — and that the curtain on modern terrestrial life may have risen far earlier than expected.

This is not just important in itself. It also pushes the whole early evolutionary history of tetrapods back in time.

The tracks, discovered on Taungurung Country in Victoria, Australia, by two amateur fossil hunters, contain something unmistakable: claws. “When I saw this specimen for the first time, I was very surprised,” co-author Grzegorz Niedźwiedzki said in a press release. “After just a few seconds, I noticed that there were clearly preserved claw marks.”

That detail is crucial. Claws are a hallmark of amniotes, animals that lay eggs or give birth on land without returning to water — unlike amphibians, which still rely on moist environments to reproduce.

“Claws are present in all early amniotes, but almost never in other groups of tetrapods,” said Ahlberg. “The combination of the claw scratches and the shape of the feet suggests that the trackmaker was a primitive reptile.”

Until now, the oldest known amniote fossils came from rocks around 320 million years old. But this slab is 355 million years old — pushing the appearance of amniotes back by a staggering 35 million years.

Filling the Gaps in Evolution’s Record

For a long time, paleontologists have been stymied by a mysterious gap in the fossil record known as “Romer’s Gap,” a roughly 20-million-year stretch between the Devonian and mid-Carboniferous periods where few tetrapod fossils have been found. The new footprints not only help fill this void — they also suggest that it was never really empty to begin with.

“The most interesting discoveries are yet to come,” said Niedźwiedzki. “There is still much to be found in the field.”

What makes the discovery even more compelling is that the slab comes from Gondwana, the ancient supercontinent that once encompassed today’s Southern Hemisphere continents. Until now, no amniote fossils had ever been documented from this time period in Gondwana. “The Australian footprint slab is about 50 cm across,” said Ahlberg, “and at present it represents the entire fossil record of tetrapods from the earliest Carboniferous of Gondwana.”

But it’s not just about one slab. The study also includes newly identified fossil tracks from Poland — also older than previous records, which support the idea that amniotes were already roaming the Earth long before their skeletal remains show up in stone.

Could These Tracks Be a Mistake?

One possibility is that these clawed prints were made by something else — perhaps a stem tetrapod, a creature outside the amniote family tree that independently evolved claws. But Ahlberg doesn’t think so.

“We are confident that these are not tracks of a stem tetrapod,” he said. “Our footprints, with their long slender toes and lizard-like overall shape, were definitely made by a crown-group tetrapod.”

He added that known stem amphibians, like temnospondyls, typically have only four toes on their front feet — whereas the Australian animal had five. “The footprints look like perfectly good crown amniote (probably sauropsid, i.e. primitive reptile) prints and would certainly have been identified as such if they had been found in Late Carboniferous strata.”

The only thing that would fully confirm the animal’s identity is a body fossil. But Ahlberg argues that manufacturing hypothetical animals — like a stem amniote with claws — just to protect outdated models is “bad science.”

A Faster, Deeper Origin Story

So, what does this mean for the big picture of evolution?

By comparing the shape and claw marks of the prints with genetic data from living animals, the researchers inferred that the amniote crown group must have originated not in the Carboniferous, but deep in the Devonian — possibly around the time when transitional “fishapods” like Tiktaalik and Elpistostege were still splashing through the shallows.

Their timeline suggests that tetrapods didn’t gradually crawl their way into complex vertebrates over tens of millions of years. Instead, they evolved and diversified far more quickly than once believed. “Devonian tetrapods must have been more diverse and more ‘modern’ than we have thought,” Ahlberg said.

But if they existed, where are they?

The answer, it seems, lies somewhere in the dirt. “The tetrapod fossil record is shockingly incomplete,” Ahlberg said. “To put things in context, our Australian slab, about 35 cm wide, is at the moment the only tetrapod fossil from the Tournaisian (earliest Carboniferous) of the whole of the giant supercontinent Gondwana!”

“The picture that emerges is that tetrapods evolved and diversified more quickly than we have thought, but that their early fossil record is even more incomplete than we had realized,” Ahlberg told me in an email.

More Discoveries Are Waiting

The scientific significance of this single slab is immense. But it also tells a deeply human story — one of curiosity, chance, and perseverance.

Craig Eury, one of the fossil’s discoverers alongside his friend John Eason, isn’t a paleontologist. But he knew he’d found something unusual. “He has no academic background in palaeontology,” Ahlberg said, “but he’s very observant and has a sharp mind; it’s been a pleasure to introduce him to the science.”

The discovery is also a reminder that the fossil record — despite its grandeur — is still mostly unwritten.

Every time scientists believe they’ve mapped out the story of evolution, a new footprint appears to lead them in another direction.

“The footprints from Australia are just one example,” said Niedźwiedzki. “The most interesting discoveries are yet to come and that there is still much to be found in the field.”

The findings appeared in the journal Nature.