The tracks, which are each about four centimetres long, were left by reptiles living 500 kilometres from the nearest seashore. ((Courtesy of University of Bristol))

An accidental discovery along the eroding Bay of Fundy shoreline in New Brunswick is giving scientists insight into the evolution of life on earth.

Scientists have discovered 318 million-year-old reptile footprints in rock slabs that have broken free of the sea cliffs, and say they show reptiles were the first vertebrates — animals with a backbone — to move inland away from the swampy coasts.

The footprints were discovered by Howard Falcon-Lang of Royal Holloway, University of London during a trek along the coast near St. Martins, N.B., in August 2008.

However, the results of his study — conducted along with Mike Benton at the University of Bristol and Canadian colleagues — are only being published Friday in the journal Palaeogeography, Palaeoclimatology, Palaeoecology after undergoing peer review.

"It's a very significant event in the history of life," Falcon-Lang said in an interview.

"About 400 million years ago, animals with backbones started to come on land, but these were frog-like creatures. And amphibians such as frogs have to return to the water in order to breed. They lay soft eggs that very easily dry out."

But Falcon-Lang said when the reptiles came along, they laid eggs with hard shells that they could lay on land, and could therefore start moving away from the shore.

Environment like central Australia

"What we found in New Brunswick is evidence of early reptiles living around a water hole in a very dry environment," he said.

'These are quite remarkable,' said Randy Miller, provincial paleontologist at the New Brunswick Museum. 'It's not just one set of footprints. The slabs are covered with footprints.' ((Courtesy of University of Bristol))

"It's a bit like environments that you might find in central Australia today."

At that time, all the continents were joined together in a single continent called Pangaea.

He said the tracks were left by reptiles living 500 kilometres from the nearest seashore.

"It's a bit like the story of the American pioneers setting westward to seek fame and fortune," said Falcon-Lang. "These early reptiles were moving into the continental interiors, exploiting environments where animal life had not been before."

Randy Miller, the provincial paleontologist at the New Brunswick Museum in Saint John, was with Falcon-Lang when the tracks were discovered.

'Covered with footprints'

"These are quite remarkable," he said Thursday. "It's not just one set of footprints. The slabs are covered with footprints."

Miller said he actually had his back to the slab and was examining plant fossils when the footprints were discovered.

Falcon-Lang said he was looking for something else, and only discovered the prints after he tripped and fell, scraping his knee.

"I still have the scars to prove it," he said.

The footprints are quite small — only about four centimetres long. Falcon-Lang said the reptile that made them would have been about 20 centimetres long and resembled a gecko.

He said it is probably an early reptile called Hylonomus. Fossil skeletons have been found in adjacent Nova Scotia.

"It's a very key step in evolutionary history, because these tiny, small, scampering gecko-like reptiles were the ancestors of dinosaurs and they were the ancestors of you and me," he said.

'Foundations for everything to come later'

"They were actually laying the foundations for everything to come later in the history of life on land."

At the time, the area now known as New Brunswick was along the equator and had a tropical ecosystem.

It's believed the footprints were made in sticky mud near a water hole shortly before a torrential rainfall. Even the marks left by the large raindrops have been preserved.

Falcon-Lang said it's like looking at a snapshot taken 318 million years ago.

"It really is that extraordinary," he said. "You're capturing an event that probably just took a few minutes."

Miller has made latex copies of the slab and pieces of the actual rock have been removed for safe-keeping at the museum in Saint John.