Fossil Hunters Discover Earliest Known Footprints of a Reptile-Like Creature, Pushing Back the Timeline of Their Evolution A new study suggests two fossil trackways found in Australia were made by an early amniote, a group that today includes reptiles, birds and mammals Amateur fossil hunters discovered a trackway left by a creature that might have looked like the one in this illustration. The finding raises new questions about the evolution of the earliest reptiles. Marcin Ambrozik Scientists in Australia have identified the earliest known tracks of a reptile-like animal, suggesting these creatures walked the Earth millions of years longer than thought. The two trackways were spotted by builder Craig Eury and winemaker John Eason, who were fossil hunting along a river bed in eastern Victoria, Australia. “It was literally the footprints that caught my eye—the light hit the rock in a way that cast a shadow on the footprints,” Eury tells Jacinta Bowler and Annie Brown at the Australian Broadcasting Corporation. Both are now listed as co-authors on a new study of the fossils, published in the journal Nature last week.  John Long, a paleontologist at Flinders University in Australia and the study’s lead author, had enlisted amateur paleontologists such as Eury and Eason to look for fossils in the area. He was shocked when he saw what the two had found. The prints appeared to be from an early four-legged creature classified as an amniote, or an animal with eggs that contain “amniotic membranes” to protect the fetus. While the earliest amniotes looked like lizards, they ultimately gave rise to the branches on the animal evolutionary tree that became today’s reptiles, birds and mammals. Eason and Eury “hit the mother lode with this trackway,” says Long to Joel Achenbach at theWashington Post. “This is the oldest evidence in the world of amniote trackways—the lineage that will eventually end up as humans. It’s huge.” The scientists dated the fossil to between 354 million and 359 million years ago, which would mean that amniotes existed at least 35 million years earlier than previously thought. That places the creatures as having lived during the early Carboniferous period, a time when Earth was covered in trees, and vast deposits of coal were beginning to form. To conduct their study, researchers analyzed the two discovered trackways, which criss-cross on a 14-inch sandstone slab. The fossilized rock is covered in dimples from raindrops, hinting at a shower just before the tracks were made—and indicating the amniotes were likely moving on dry land, as some of the paper’s authors write in an article for the Conversation. The footprints also have claw marks, which are not seen in amphibian tracks, and they’re five-toed, another sign that points to amniotes. Some of them left long scratches from dragging the foot. 350 million year old reptile tracks Watch on Anthony Romilio, a paleontologist at the University of Queensland in Australia who was not involved in the study, disagrees with the assumption that the creatures were on land. “I see [tracks like these claw-like marks] across a variety of different animals, when the animal is supported by water,” he says to the Australian Broadcasting Corporation. For instance, the animals could have made the tracks by pushing off the ground in shallow water, then gliding until they landed to push off again, in a motion known as “punting,” as Steven Salisbury, a paleontologist at the University of Queensland, tells Nature’s Rita Aksenfeld. Long, however, stands behind his work. “In our opinion … the sharp claws digging in the second trackway are too precise to suggest they were digging or clawing the sediment underwater,” he adds to the Australian Broadcasting Corporation. The scientists also identified similar tracks found in Poland. Those tracks are slightly younger but are still record-breaking: They’re the oldest known reptile-like tracks in Europe, per the Conversation. Key questions about the track maker remain unanswered from the footprints alone. What the creature looked like, its exact size and traits such as whether or not it had a tail can’t be revealed by a trackway. To verify their findings, the researchers will have to “find body fossils—bones from these rocks—that can confirm the presence of amniotes so long ago,” says Erich Fitzgerald, a senior curator of vertebrate paleontology at Museums Victoria Research Institute who was not involved in the work, to Petra Stock at the Guardian. Nevertheless, he adds it is a “provocative discovery with potentially far-reaching implications.” Per Ahlberg, a paleontologist at Uppsala University in Sweden and a co-author of the study, tells the Washington Post that footprints, in general, are useful to paleontologists. “Footprints are fossil movie clips of living animals. You’re not looking at dead remains,” he says. “You’re looking at live animals doing their stuff.” Get the latest stories in your inbox every weekday.