May 15, 20253 min readNewly Discovered Fossil Tracks May Rewrite Early History of ReptilesFossilized claw tracks discovered in Australia show that the animal group that includes reptiles, mammals and birds formed earlier than expectedBy Rita Aksenfeld & Nature magazine Illustration of an amniote animal thought to have left fossilized claw prints in Victoria, Australia. Marcin AmbrozikFossil claw prints found in Australia were probably made by the earliest known members of the group that includes reptiles, birds and mammals, according to a study published in Nature today. The findings suggest that this group — the amniotes — originated at least 35 million years earlier than previously thought.Early amniotes evolved to lay eggs on land, because they were encased in an amniotic membrane that stopped them drying out. Before this study, the earliest known amniote fossils had been found in Nova Scotia, Canada, and were dated to the mid-Carboniferous period, about 319 million years ago. The latest findings suggest that amniotes also existed in the early Carboniferous period, around 355 million years ago.“This discovery is exciting, and if the tracks have been interpreted the right way, the findings have important implications for our understanding of tetrapod evolution,” says Steven Salisbury, a palaeontologist at the University of Queensland in Brisbane, Australia.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.The tracksThe claw tracks were found in a sandstone block on the bank of the Broken River at Barjarg in the state of Victoria, by two co-authors of the paper who are not professional scientists. This area of the river is known as Berrepit to the Indigenous Taungurung people who own the land.The sandstone block is part of a larger structure that had already been dated to the early Carboniferous on the basis of radiometric and tectonic evidence. Fossilized tracks of aquatic invertebrates and fish found in the same layer were also dated to this time period.The Snowy Plains Formation trackway slab with footprints and trackways highlighted. Manus (front foot) prints are shown in yellow; pes (hind foot) prints are shown in blue.Grzegorz NiedzwiedzkiThe three sets of tracks in the study have clear footprints with indentations from claws, a feature of reptiles but not of amphibians. “Having these hooked claws on the trackways indicates they’re definitely a reptile-like animal,” says John Long, a palaeontologist at Flinders University in Adelaide, Australia.There are no marks of dragging bellies or tails, and the authors suggest that the amniotes that left the tracks were able to keep their bodies and tails off the ground while they walked on land. But Salisbury questions that interpretation, because it would mean the animals had developed sophisticated structures for complex locomotion, which would be surprising given how early they are. “It seems more likely that the tracks were made by an animal that was ‘punting’ in shallow water, rather than walking on land,” he says.Common ancestorUntil now, evidence suggested that the last common ancestor of modern amphibians and amniotes lived around 352 million years ago. But if the ancestors of reptiles existed during the early Carboniferous, their split from amphibians must have occurred even earlier, says Long. Dating by the team suggests that the groups diverged in the Devonian period, about 380 million years ago.To estimate the probable time of divergence, Long and his colleagues used several dating methods. One included geological evidence from radioactive decay in volcanic rock layers above and below the fossil tracks. They also used molecular phylogenetics, which compares similarities and differences in the DNA of living species to estimate their evolutionary relationships and how recently their last common ancestor lived.The discovery could also shift the origin of amniotes to the Gondwana landmass. This formed the southern portion of the Pangaea supercontinent and gave rise to multiple current landmasses, including Africa and Australia. Previously, the earliest known amniotes were found in North America, leading palaeontologists to think that the group originated in the Northern Hemisphere. But more evidence from Australian fossils is needed before definitively shifting their origin site, says Long. “Australia is a vast area with fewer palaeontologists on the ground,” Long says. “We’ve got a lot more unexplored fossil sites where new things like this keep turning up.”This article is reproduced with permission and was first published on May 14, 2025.

Australia and South America weren’t always so separate. At one time, many millions of years ago, these two continents were connected, along with others, in the southern supercontinent of Gondwana. Gondwana was a warm, forested place — a perfect home for tree frogs. In fact, the supercontinent fostered the common ancestor of the Australian pelodryadid frogs and the South American phyllomedusid frogs that are still seen, stuck to leaves and branches, today. But when did this common tree frog ancestor appear, and when did it diverge into these two separate frog families?A new study published in the Journal of Vertebrate Paleontology provides some answers. Identifying a new species of Australian tree frog from the Early Eocene around 55 million years ago, the study suggests that the Australian and South American tree frog lineages split apart at around that time, too, or even earlier than that. All in all, the study rethinks the timeline of tree frog evolution and suggests that these lineages are a lot older than traditionally thought.The Australian-South American Frog SeparationTo be sure, the new study isn’t the first to investigate the divergence of the Australian and South American tree frogs. By following the genetic transformations of these two families over time, prior molecular studies have shown, for instance, that the pelodryadids and the phyllomedusids split apart approximately 33 million years ago.The fossil record has supported that timing in the past, with the earliest Australian tree frog fossils previously appearing in Australia after 33 million years ago, in the Late Oligocene and the Early Miocene epochs about 26 and 23 million years ago. But the new species undermines this timeline, suggesting that the separation of Australian and South American tree frogs actually occurred around 55 million years ago at a minimum, or at least around 22 million years earlier than previously thought. The new species, named Litoria tylerantiqua, is now the earliest identified species of Australian tree frog there is. Represented by fossilized pelvic bones from the Murgon fossil site in Queensland, Australia, the pelodryadid species is approximately 55 million years old, or about 30 million years older than any other Australian tree frog found in the fossil record. “While molecular studies are important for understanding the evolutionary relationships of different groups of animals, these studies should be calibrated using knowledge from the fossil record,” said Roy Farman, the lead study author and a lecturer at the University of New South Wales, according to a press release. “In this case, the fossil record provides a more accurate time for separation of the southern world’s tree frogs.”Tree Frogs, Fossilized and PickledThree fossilized ilia (pelvic bones) represent a new species of Australian tree frog, Litoria tylerantiqua. (Image Credit: UNSW Sydney/Roy Farman) To confirm the species’ identification as a pelodryadid, the study authors compared the pelvises of the new species with the pelvises of pickled frogs, including Australian and South American tree frogs, from museums in Australia. “We were able to determine from the shape of the fossil ilia — one of three bones that make up each side of the pelvis — that this new Murgon species of frog is more closely related to the Australian tree frogs (pelodryadids) than the South American tree frogs (phyllomedusids),” Farman said in the release. Though the structure of the pelvic bones from the new species was relatively simple to study, the structure of the bones from the pickled species was not. “We had a real problem at the start of this study,” Farman added in the release, because the bones of the pickled specimens were “invisible,” being obscured by the specimens’ soft tissues. “Museums understandably want to ensure these often unique or rare pickled specimens remain intact for molecular studies because DNA can be obtained from their soft tissues,” Farman said in the release. “This meant that instead of [skeletonizing] these specimens, we needed instead to make CT scans of them, enabling us to create 3D models of their otherwise invisible skeletons.”The new species is named after the Australian herpetologist Michael Tyler, who was famous for studying the fossil record of Australian frogs and toads. “It is only fitting to name Australia’s earliest tree frog in [honor] of a man who was a giant in Australian frog research,” Farman said in the release. Article SourcesOur writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:Sam Walters is a journalist covering archaeology, paleontology, ecology, and evolution for Discover, along with an assortment of other topics. Before joining the Discover team as an assistant editor in 2022, Sam studied journalism at Northwestern University in Evanston, Illinois.

An illustration of what the Amniote (early reptile) would look like from 350 million years ago. CREDIT: Martin Ambrozik. Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent every weekday. One of the most impactful stories in evolution is getting a rewrite, thanks to the exciting discovery of the earliest known set of reptile footprints. Craig A. Eury and John Eason, two amateur paleontologists exploring the fossil-rich Snowy Plains Formation in Australia, found a rock with an intriguing set of fossilized prints. They brought the intriguing specimen to professional paleontologists, who soon discovered that the roughly 356 million-year-old fossilized claw prints likely belong to an amniote–an early reptile relative.  Though small in stature, amniotes were a large evolutionary leap forward towards land-dwelling, four-limbed animals called tetrapods. The age of these prints suggest that amniotes evolved millions of years earlier than expected, according to a study published May 14 in the journal Nature.  “I’m stunned,” Per Ahlberg, a paleontologist at Uppsala University in Sweden who coordinated the study, said in a statement. “A single track-bearing slab, which one person can lift, calls into question everything we thought we knew about when modern tetrapods evolved.” When fish grew legs Tetrapods include all vertebrates with four limbs that primarily live on land, including everything from frogs to turtles to eagles, to tigers to humans. Their story began as fish left the water between 390 and 360 million years ago. Their descendants began to diversify into the ancestors of modern amphibians and amniotes–the group that includes birds, reptiles, and mammals. Originally, the timeline for how this massive diversification of life occurred was fairly clear-cut. The first tetrapods evolved roughly 390 million years ago during the Devonian period. Amniotoes and the earliest members of the modern groups of animals we see today followed fishapods during the Carboniferous period. Previously, the earliest amniote fossils dated back to  about 320 million years old to the late Carboniferous. Based on this new evidence, researchers concluded the start of the point on the evolutionary tree where the ancestors of amphibians and amniotes split actually happened in the earliest days of the Carboniferous or 356 million years ago.   Proof in the prints The newly discovered 356 million-year-old sandstone slab from this new study potentially changes this entire timeline by about 35 to 40 million years. The well-preserved footprints of long-toed feet with distinct claw impressions at the tips dot the stone and are the earliest known clawed footprints. Two sets of tracks were identified on the stone, seemingly from the same animal.  Footprints are important for paleontologists, as they can indicate the types of behaviors an extinct animal may have exhibited. The team compared the ancient tracks with a modern water monitor (Varanus salvator) lizard, since they have similarly shaped feet to what is seen on the footprints. They examined the spacing between the front and hind footprints against that living lizard’s feet. With these measurements, the team estimates that the ancient amniote may have been around 2.5 feet long, but that the exact proportions of the animal are still unknown. “Claws are present in all early amniotes, but almost never in other groups of tetrapods,” Ahlberg said. “The combination of the claw scratches and the shape of the feet suggests that the track maker was a primitive reptile.” If this new interpretation is correct, it pushes the origin of reptiles, and thus amniotes as a whole, back by roughly 40 million years to the earliest Carboniferous. A new set of fossil reptile footprints uncovered all the way across the globe in Poland are also detailed in the study and bolster the evidence. These European footprints are not as old as the ones from Australia, but are still older than previous specimens.  “The implications of this discovery for the early evolution of tetrapods are profound,” John Long, a study co-author and paleontologist at Flinders University in Australia, said. “All stem-tetrapod and stem-amniote lineages must have originated during the Devonian period – but tetrapod evolution proceeded much faster, and the Devonian tetrapod record is much less complete than we have believed.” A place on the evolutionary tree According to the team, this recalibration of the origin of reptiles has a ripple effect on the whole timeline of tetrapod evolution. Tetrapods must be older than even the earliest amniotes, since it has a deeper branching point on the evolutionary tree.  “It’s all about the relative length of different branches in the tree,” said Ahlberg. “In a family tree based on DNA data from living animals, branches will have different lengths reflecting the number of genetic changes along each branch segment. This does not depend on fossils, so it’s really helpful for studying phases of evolution with a poor fossil record.” The fossil trackways with the different tracks on it highlighted. CREDIT: Flinders University The team believes that amphibians and ammonites split apart further into the Devonian period and were likely a contemporary of the primitive, transitional “fishapod” called Tiktaalik. This evidence indicates that a diverse group of tetrapods existed when only transitional “fishapods” were believed to be dragging themselves around muddy shorelines and starting to explore the land.  If this new theory holds, it is likely that the evolution of tetrapods from aquatic creatures to those fully living on land may have occurred even faster than previously believed.   “The Australian footprint slab is about 50 cm [1.5 feet] across,” said Ahlberg, “and at present it represents the entire fossil record of tetrapods from the earliest Carboniferous of Gondwana – a gigantic supercontinent comprising Africa, South America, Antarctica, Australia and India. Who knows what else lived there?”   “The most interesting discoveries are yet to come and that there is still much to be found in the field,” added study co-author and paleontologist Grzegorz Niedźwiedzki. “These footprints from Australia are just one example of this.” 

Underneath miles-deep ice sheets covering Antarctica lies the largest mountain range no one on Earth has ever seen. Even though a few of its tallest points peek through in some places, relatively few people know of the entire range’s existence.However, geologists studying it have long argued about how and when these buried peaks were formed. A team of geologists propose a new explanation in an article in the journal Earth and Planetary Science Letters.“The ice conceals some of Earth’s most enigmatic features,” according to the paper. One such feature is the Gamburtsev Subglacial Mountains, which rises over 9,000 feet above sea level and is covered by about 10,000 feet of ice. Its highest point is considered the coldest place on Earth. The range is equivalent in size and shape to the Swiss alps.Creation of the Antarctica MountainsMany geologists think these features were created when multiple tectonic plates that include what is now known as Africa, South America, Australia, India, and Antarctica collided to create a supercontinent called Gondwana. However, beyond that event, there is less agreement.“...the timing and three-dimensional structure of the collisional zone, known as the Kuunga Orogen, remain highly controversial,” according to the paper.The new study provides a bit more detail. The authors propose that the tectonic plates collision first uplifted the Gamburtsev Mountains when they had ground together. The tectonic collision then unleashed a flow of molten rock beneath the mountains. As that molten layer became hotter and thicker, the mountains above it collapsed under their own weight. The base of the mountains now rest upon the Earth’s mantle, the layer beneath the planet’s crust.Rock Beneath the Ice SheetThe geologists tracked this massive activity by looking at tiny objects — zircon grains deposited by rivers flowing from the mountains more than 250 million years ago. These grains act as geologic timers, because they contain uranium, which decays at a rate scientists can use to measure their age.According to the grains found at various points of the range, the mountains begin their rise about 650 million years ago, reached Himalayan heights by 580 million years ago, then completed their sinking by about 500 million years ago. A massive layer of ice has covered them since, making them one of the best preserved mountain ranges on the planet, because the ice shields them from the erosion that wears down more exposed mountains.The scientists could learn more about the range’s composition by drilling through the ice to extract rock samples. However, that is a long and expensive process. They are now looking at exposed rocks from Antarctica’s east coast to get a hint of what kinds of rock might lie beneath the massive ice sheet.Article SourcesOur writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:Earth and Planetary Science Letters. Gondwanan continental collision drives gravitational spreading and collapse of the ancestral East Antarctic mountainsBefore joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.

Researchers reviewed ocean floor samples collected during the Deep Sea Drilling Project in 1975. Credit: Deposit Photos / Oleg Dorokhin Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent every weekday. There was a time long ago when the Atlantic Ocean didn’t exist. The general understanding among geologists is that the body of water originated between 83 to 113 million years ago, when South America and Africa split into their two respective continents to form the Equatorial Atlantic Gateway. However, Earth’s marine history appears to require a multimillion-year revision thanks to a recent discovery roughly half a mile beneath the ocean floor. The evidence is explored in a study published in the June edition of the journal Global and Planetary Change. According to geologists at the UK’s Heriot Watt University, gigantic waves of mud and sand sediment about 250 miles off the coast of Guinea-Bissau in West Africa indicate the Atlantic Ocean actually formed around four million years earlier than previous estimates. To understand just how intense all of this movement was, imagine waves that are about half a mile long and over 300 feet high.  “A whole field formed in one particular location to the west of the Guinea Plateau, just at the final ‘pinch-point’ of the separating continents of South America and Africa,” study co-author Uisdean Nicholson explained in a statement. Nicholson and their colleagues initially came across these layers of mud waves after comparing seismic data with core samples collected from wells during the Deep Sea Drilling Project (DSDP) of 1975. Five layers in particular were utilized to recreate the tectonic processes that broke apart the ancient supercontinent of Gondwana during the Mesozoic Era. “One layer was particularly striking: it included vast fields of sediment waves and ‘contourite drifts’—mud mounds that form under strong bottom currents,” said Nicholson. These waves initially formed as dense, salty water poured out from the newly created Equatorial Atlantic Gateway, “like a giant waterfall that formed below the ocean surface,” he added. Just before the geologic event, huge salt deposits formed at the bottom of what is now the South Atlantic. After the gateway opened, the underground mudfall occurred when dense, relatively fresh Central Atlantic water in the north combined with very salty waters in the south. The resulting sedimentary evidence examined by the study’s authors now indicates this opening seems to have started closer to 117 million years ago. “This was a really important time in Earth’s history when the climate went through some major changes,” explained study co-author Débora Duarte. “Up until 117 million years ago, the Earth had been cooling for some time, with huge amounts of carbon being stored in the emerging basins, likely lakes, of the Equatorial Atlantic. But then the climate warmed significantly from 117 to 110 million years ago.” Duarte and Nicholson believe part of that major climatic change  helped from the Atlantic Ocean, as seawater inundated the newly formed basins. “As the gateway gradually opened, this initially reduced the efficiency of carbon burial, which would have had an important warming effect,” said Duarte. “And eventually, a full Atlantic circulation system emerged as the gateway grew deeper and wider, and the climate began a period of long-term cooling during the Late Cretaceous period.” The ramifications go beyond revising Earth’s geological timeline or the gateway’s role in Mesozoic climate change. Better understanding the influence of oceanic evolutionary journeys on ancient climate patterns can help to predict what the future holds for the planet.  “Today’s ocean currents play a key role in regulating global temperatures,” explained Nicholson. “Disruptions, such as those caused by melting ice caps, could have profound consequences.”