Earliest-known 'reptile' footprints discovered by amateur fossil hunters in Victoria

Builder Craig Eury and winemaker John Eason were fossil hunting near the Victorian town of Mansfield when they spotted some footprints on a slab of rock.

"It was literally the footprints that caught my eye — the light hit the rock in a way that cast a shadow on the footprints," Mr Eury said.

The footprints they discovered back in 2021 were made by an amniote — an early relative of reptiles, birds, and mammals — according to a study published today in the journal Nature.

John Long, a palaeontologist at Flinders University who led the study, said the fossil could help scientists understand when our animal ancestors first left the water to become land dwellers.

"It's the [evolutionary] line that leads to us," Professor Long said.

Claws 'dead giveaway' for amniote

Mr Eury and Mr Eason — both study co-authors — discovered the footprints on the bank of Broken River in Taungurung country in the foothills of the Victorian Alps.

Dated to be approximately 356 million years old, the trackway is 40 million years older than previous fossils.

This means reptile-like creatures were walking on land in the earliest Carboniferous Period, a time when vast swamp forests dominated Earth and most animals, like amphibians, lived at least partially in water.

Claw imprints in the trackway were the "dead giveaway" that the footprints did not belong to an amphibian, according to Professor Long.

"It's a characteristic of terrestriality, because it often implies you're climbing trees, or you need the claws of for digging … that amphibians just don't normally do."

Anne Warren, an emeritus professor of palaeontology at La Trobe University who was not involved with the research, agrees.

"This new track is undoubtedly from an amniote because there are five digits on the front foot, and these are clawed. In amphibians, there are four anterior digits without claws," she said.

"The find is of immense importance to our understanding of when and where the main vertebrate [group] evolved."

Not only is the fossil the earliest-known amniote, but Professor Long believes it may be evidence of the earliest-known reptile.

"It's almost certain that what we have are the earliest reptile trackways," he said.

Did the animal walk or swim?

The textbook-sized sandstone block shows two sets of tracks travelling in the same direction, one with well-defined paw prints and one with less-defined, claw-like marks.

The team suggests the well-defined footprints were made first and the claw marks came later when the ground had begun to harden.

But Anthony Romilio, a University of Queensland palaeontologist who specialises in trackways not involved in the study, was not so certain.

He suggests the animal may have been swimming, not walking.

"I see [tracks like these claw-like marks] across a variety of different animals, when the animal is supported by water," Dr Romilio said.

However, Professor Long disagrees.

"All of these thoughts were raised by reviewers and weighed up," he said.

"In our opinion … the sharp claws digging in the second trackway are too precise to suggest they were digging or clawing the sediment underwater."

More fossils from the same area and time frame might shed more light on the reptile-like creature, and whether it was walking or swimming through the mud.

Mansfield region could yield more fossils

According to Professor Long, more finds are likely in the area known as the Snowy Plain Formation.

"Certainly, the area is so vast that there is potential to find more of these trackways or even the bones of these creatures," he said.

This discovery is particularly special for Professor Long, who has a long-time connection to the location where the fossils were found.

"I'm so excited by this discovery because it comes from an area that I did my PhD and my honours thesis on 45 years ago," he said.

"You've got this big, vast area of red carboniferous rocks in the basin there in Mansfield and you can still find world-class fossils there."

Years ago, Professor Long started giving talks at the local Mansfield library about the area's fossils and had even gone on field trips out to the sites.

"You plant the seed and encourage people to go out looking, and eventually they find something truly wonderful," Professor Long said.

Mr Eason had been among those that had attended back in 2008 and retained his interest in fossil hunting, bringing Mr Eury into the fold.

Mr Eury said he found the experience "surreal".

He travelled to Sweden with the trackway so researchers from Uppsala University could study them.