Australian scientists identified the oldest fossilized footprints of a reptile-like animal on a sandstone slab found near Melbourne. Discovered by Professor John Long and colleagues after being alerted by locals to something remarkable near Mansfield, Victoria, the tracks date back approximately 350 million years to the Carboniferous period. The footprints record a series of events in one day, with a reptile running quickly across the ground. Scientists estimate the animal that made the footprints was about 80 centimeters long and may have looked like a modern monitor lizard.
"This is the world's oldest evidence of land-walking reptile-like animals," said Professor John Long, a paleontologist from Flinders University in Australia, noting that previous records from the Northern Hemisphere were thought to be 35 to 40 million years younger.
The fossil footprints were found on a slab of sandstone that contains three sets of tracks believed to have been made by the same species of tetrapod, or four-legged animal. The ancient footprints show reptile-like feet with long toes and curved claws, with distinct claw impressions at the tips. "The combination of the claw scratches and the shape of the feet suggests that the track maker was a primitive reptile," said Professor Per Ahlberg, a paleontologist at Uppsala University in Sweden.
"We can see beautiful, five-fingered hands and hooked claws in these new trackways," John Long said, according to New Scientist.
Curved claws are an important clue for identification. "This is a walking animal," co-author Per Ahlberg stated. The researchers note that only animals that evolved to live entirely on land developed claws or nails.
The discovery suggests that after the first animals evolved onto land about 400 million years ago, they developed the ability to live entirely on land much faster than previously hypothesized, pushing back the timeline of terrestrial life by millions of years. This finding challenges existing theories about the evolutionary journey from fin to limb. "We thought the transition from fin to limb took much longer than the evidence now suggests," remarked Stuart Sumida, a paleontologist. "This is the earliest evidence we've ever seen of an animal with claws."
At the time this ancient reptile lived, the area was hot and humid, with extensive forests beginning to cover the planet, leaving much of it to invertebrates. Australia was part of the supercontinent Gondwana, which included Africa, South America, Antarctica, and India.
The age of these prints suggests that amniotes evolved millions of years earlier than previously expected, rewriting the timing on when the clade that includes mammals first evolved. Based on the new evidence, researchers concluded that the split between the ancestors of amphibians and amniotes occurred around 356 million years ago, in the earliest days of the Carboniferous, although the timing of amniote history is much more uncertain.
"This discovery pushes back the origin of amniotes by at least 35 million years, providing confirmation for amniotes' earlier emergence," stated IFLScience.
The footprint slab is covered with dimples made by raindrops, indicating a brief shower just before the footprints were made. "We show that raindrops fell and left impressions on the surface. Then the creatures walked across it, leaving crisp prints over the raindrops," John Long explained.
"I'm stunned. A single track-bearing slab, which one person can lift, calls into question everything we thought we knew about when modern tetrapods evolved," said Professor Per Ahlberg.
Tetrapods originated in the Devonian period, around 390 million years ago, when lobe-finned fishes began to haul themselves out of the water. The emergence of four-legged animals known as tetrapods was a key step in the evolution of many species today, including humans.
The article was written with the assistance of a news analysis system.