Fossil tracks show reptiles appeared on Earth up to 40 million years earlier
image:
Dr Aaron Camens, Professor John Long and Dr Alice Clement with a replica of the fossil trackways at Flinders University's Palaeontology Lab.
view moreCredit: Flinders University
The origin of reptiles on Earth has been shown to be up to 40 million years earlier than previously thought – thanks to evidence discovered at an Australian fossil site that represents a critical time period.
Flinders University Professor John Long and colleagues have identified fossilised tracks of an amniote with clawed feet – most probably a reptile – from the Carboniferous period, about 350 million years ago.
“Once we identified this, we realised this is the oldest evidence in the world of reptile-like animals walking around on land – and it pushes their evolution back by 35-to-40 million years older than the previous records in the Northern Hemisphere,” says Professor Long, Strategic Professor in Palaeontology at Flinders.
Published today in the journal Nature, this discovery indicates that such animals originated in the ancient southern supercontinent of Gondwana, of which Australia was a central part
The fossil tracks, discovered in the Mansfield district of northern Victoria in Australia, were made by an animal that Professor Long predicts would have looked like a small, stumpy, Goanna-like creature.
“The implications of this discovery for the early evolution of tetrapods are profound,” says Professor Long.
“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.”
Fossil records of crown-group amniotes – the group that includes mammals, birds and reptiles – begin in the Late Carboniferous period (about 318 million years old), while previously the earliest body fossils of crown-group tetrapods were from about 334 million years ago, and the oldest trackways about 353 million years old.
This had suggested the modern tetrapod group originated in the early Carboniferous period, with the modern amniote group appearing in the early part of the Late Carboniferous period.
“We now present new trackway data from Australia that falsify this widely accepted timeline,” says Professor Long, who worked with Australian and international experts on the major Nature journal paper.
“My involvement with this amazing fossil find goes back some 45 years, when I did my PhD thesis on the fossils of the Mansfield district, but it was only recently after organizing palaeontology field trips to this area with Flinders University students that we got locals fired up to join in the hunt for fossils.
“Two of these locals – Craig Eury and John Eason (coauthors on the paper) – found this slab covered in trackways and, at first, we thought they were early amphibian trackways, but one in the middle has a hooked claw coming off the digits, like a reptile – an amniote, in fact.
“It was amazing how crystal clear the trackways are on the rock slab. It immediately excited us, and we sensed we were onto something big – even though we had no idea just how big it is.”
The Flinders palaeontology team working on this project included Dr Alice Clement, who scanned the fossil footprints to create digital models that were then analysed in detail, working closely with a team from Uppsala University led by Professor Per Erik Ahlberg, a member of the Royal Swedish Academy of Sciences.
“We study rocks and fossils of the Carboniferous and Devonian age with specific interest to observe the very important fish-tetrapod transition,” says Dr Clement.
“We’re trying to tease apart the details of how the bodies and lifestyles of these animals changed, as they moved from being fish that lived in water, to becoming tetrapods that moved about on land.”
Another coauthor Dr Aaron Camens, who studies animal trackways from around Australia, produced heatmaps that explain details of the fossil footprints much more clearly.
“A skeleton can tell us only so much about what an animal could do, but a trackway actually records its behaviour and tells us how this animal was moving,” says Dr Camens.
Because Professor Long had been studying ancient fish fossils of this area since 1980, he had a clear idea of the age of rock deposits in the Mansfield district – from the Carboniferous period, which started about 359 million years ago.
“The Mansfield area has produced many famous fossils, beginning with spectacular fossil fishes found 120 years ago, and ancient sharks. But the holy grail that we were always looking for was evidence of land animals, or tetrapods, like early amphibians. Many had searched for such trackways, but never found them – until this slab arrived in our laboratory to be studied.
“This new fossilised trackway that we examined came from the early Carboniferous period, and it was significant for us to accurately identify its age – so we did this by comparing the different fish faunas that appear in these rocks with the same species and similar forms that occur in well-dated rocks from around the world, and that gave us a time constraint of about 10 million years.”
La Trobe University's Dr Jillian Garvey, who liaised with the Taungurung Land and Waters Council for the study, has researched in the Mansfield basin since the early 2000s.
"This discovery rewrites this part of evolutionary history," Dr Garvey says. "It indicates there is so much that has happened in Australia and Gondwana that we are still yet to uncover."
The research – ‘Earliest amniote tracks recalibrate the timeline of tetrapod evolution’ (2025) by John A Long, Grzegorz Niedźwiedzki, Jillian Garvey, Alice M Clement, Aaron B Camens, Craig A Eury, John Eason and Per E Ahlberg (Uppsala University) – has been published in Nature. DOI: 10.1038/s41586-025-08884-5
Available online: https://www.nature.com/articles/s41586-025-08884-5
Videos and images: Fossil tracks show reptiles appeared on Earth up to 40 million years earlier - Google Drive
Journal
Nature
Method of Research
Computational simulation/modeling
Subject of Research
Animals
Article Title
Earliest amniote tracks recalibrate the timeline of tetrapod evolution
Article Publication Date
14-May-2025
Caption
Graphic depicting the age range of the slabs where the fossil trackways were found.
Credit
Flinders University
3D animation recreation of the reptile trackways 350 million years ago, as well as the age of the rock slabs where this discovery was found.
Earliest reptile footprints rewrite the timeline of tetrapod evolution
Uppsala University
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The image shows a reconstruction of the reptile. Illustration: Marcin Ambrozik
view moreCredit: Marcin Ambrozik
"I'm stunned." says Per Ahlberg of Uppsala University, who coordinated the study; "A single track-bearing slab, which one person can lift, calls into question everything we thought we knew about when modern tetrapods evolved."
The story of the origin of tetrapods began with fishes leaving the water, and ended with the descendants of these first colonists on land diversifying into the ancestors of the modern amphibians and amniotes (the group that includes reptiles, birds and mammals). The timeline of these events has seemed clear-cut: the first tetrapods evolved during the Devonian period and the earliest members of the modern groups appeared during the following Carboniferous period. The earliest amniote fossils are from the late Carboniferous, about 320 million years old. This led researchers to conclude that the beginning of the evolutionary radiation of the modern groups, the point on the evolutionary tree where the ancestors of amphibians and amniotes separated (also known as the 'tetrapod crown-group node'), lay in the earliest Carboniferous around 355 million years ago. The Devonian period was seen as inhabited by more primitive fish-like tetrapods and transitional 'fishapods' such as Tiktaalik.
A sandstone slab from the earliest Carboniferous of Australia, approximately 355 million years old, discovered by two amateur palaeontologists who co-authored the study, changes all this. It carries well-preserved footprints of long-toed feet with distinct claw impressions at the tips. These are by far the earliest clawed footprints ever discovered.
“When I saw this specimen for the first time, I was very surprised, after just a few seconds I noticed that there were clearly preserved claw marks.” says Grzegorz Niedźwiedzki of Uppsala University, co-author of the study.
"Claws are present in all early amniotes, but almost never in other groups of tetrapods." adds Per Ahlberg; "The combination of the claw scratches and the shape of the feet suggests that the track maker was a primitive reptile."
If this interpretation is correct, it pushes the origin of reptiles, and thus amniotes as a whole, back by 35 million years to the earliest Carboniferous. Further support comes from new fossil reptile footprints from Poland, also presented in the study; not as old as those from Australia, but also substantially older than previous records. This recalibration of the origin of reptiles impacts the whole timeline of tetrapod evolution. The tetrapod crown-group node must be older than the earliest amniotes, because it is a deeper branching point in the tree, but how old exactly? The authors address this problem by combining data from fossils and modern DNA.
"It's all about the relative length of different branches in the tree" explains Per 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."
Their analysis, overlaying branch lengths from DNA analyses onto the known fossil dates, indicates that the tetrapod crown group node lies far back in the Devonian, roughly contemporary with Tiktaalik. This means that a diversity of advanced tetrapods existed at a time when, it has been thought, only transitional 'fishapods' were dragging themselves around muddy shorelines and starting in a small way to explore the land. But perhaps that should not surprise us.
"The Australian footprint slab is about 50 cm across", says Per 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. These footprints from Australia are just one example of this.” says Grzegorz Niedźwiedzki.
Journal
Nature
Article Title
Earliest amniote tracks recalibrate the timeline of tetrapod evolution
Article Publication Date
14-May-2025
The sandstone slab from the earliest Carboniferous of Australia, approximately 355 million years old.
Footprints of front feet (manus) are shown in yellow, hind feet (pes) in blue.
Fully labelled image of the Australian slab, showing interpretation of the tracks. Footprints of front feet (manus) are shown in yellow, hind feet (pes) in blue. The slab carries two trackways, A and B. For each of these, the footprints are coded as follows: Am1 to Am4 means “Trackway A, manus print 1” to “Trackway A, manus print 4”. Ap1 etc. means “Trackway A, pes print 1” etc.. Bm1-4 and Bp1-4 mean the same for Trackway B. Blue and yellow zig-zag lines linking prints indicate the sequence manus and pes prints in each trackway. The label “Ip” next to a white oval means “Isolated pes print”, a single footprint facing the opposite direction to the trackways.
Credit
Grzegorz Niedźwiedzk
UV light and CT scans helped scientists unlock hidden details in a perfectly-preserved fossil Archaeopteryx
Never-before-seen feathers were the key to Archaeopteryx flight
Field Museum
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The Chicago Archaeopteryx under UV light to show soft tissues alongside the skeleton.
view moreCredit: Delaney Drummond
Archaeopteryx is the fossil that proved Darwin right. It’s the oldest known fossil bird, and it helps show that all birds— including the ones alive today— are dinosaurs. And while the first Archaeopteryx fossil was found more than 160 years ago, scientists are continuing to learn new things about this ancient animal. In a new paper in the journal Nature, researchers described the features of the latest Archaeopteryx fossil to be shared with the public scientific record: the Chicago Archaeopteryx, which went on display in 2024 at the Field Museum. Thanks to the incredibly detailed work by the scientists who prepared the specimen, this fossil preserves more soft tissues and fine skeletal details than have ever been seen in Archaeopteryx. In particular, a set of feathers never before seen in this species help explain why it could fly when many of its non-bird dinosaur cousins could not.
Like all Archaeopteryx fossils, the Chicago specimen was found in limestone deposits near Solnhofen, Germany. This particular specimen was found by a private fossil collector prior to 1990, and had been in private hands since 1990. A coalition of supporters helped the Field Museum procure it; it arrived at the museum in August 2022.
“When we first got our Archaeopteryx, I was like, this is very, very, very cool, and I was beyond excited. But at the same time, Archaeopteryx has been known for over 160 years, so I wasn’t sure what new things we would be able to learn,” says Jingmai O’Connor, the Field Museum’s associate curator of fossil reptiles and lead author of the paper. “But our specimen is so well-preserved and so well-prepared that we’re actually learning a ton of new information, from the tip of its snout to the tip of its tail.”
Archaeopteryx, which lived about 150 million years ago during the Jurassic Period, was a small animal— the Chicago specimen in particular is the smallest one known, only about the size of a pigeon. Its tiny, hollow bones are preserved in a slab of extremely hard limestone. “When you have such a delicate fossil, you can’t completely remove it from the surrounding rock matrix the way you do with something big and solid like a T. rex,” says O’Connor. “So when we prepared it, we carefully chipped away the bits of rock covering the fossil.”
A team of fossil preparators, led by the Field Museum’s chief fossil preparator Akiko Shinya, spent over a year working on the Chicago Archaeopteryx. The work was incredibly detailed. Even seeing where the fossil ended and the rock matrix began was a challenge, because the preserved bones and tissues are nearly the same color as the surrounding rock. The CT scan was also used to better delineate the boundaries of the fossil.
“A CT scanner is essentially a machine that takes a series of X-rays, which it uses to build a three-dimensional image, based on differences in density. It lets you see inside things,” says O’Connor. “CT scanning was very important for our preparation process— it let us know things like, the bone is exactly 3.2 millimeters below the surface of the rock, which let us know exactly how far we could go before we would hit the bone. This is the first time a complete Archaeopteryx has been CT scanned and the data made available.”
The team was further guided by the use of UV light to illuminate pieces of the fossil’s skeleton and even its soft tissues, like scales on the bottom of the toes. “Previous studies have shown that there’s something in the chemical composition of Solnhofen fossils that makes the soft tissues fluoresce, or glow under UV light,” says O’Connor. “So our amazing prep team utilized UV light periodically through the preparation process to make sure that they weren't accidentally removing any soft tissues that you can’t see with the naked eye.”
This careful, technology-guided preparation led to more fine details being preserved in the Chicago Archaeopteryx than in any other specimen. “We’re lucky in that this specimen happens to be extremely well-preserved, but we can also see features that probably were preserved in other specimens, but which didn’t make it through cruder preparation processes in the past,” says O’Connor. “Having the preparation of this specimen done by scientists whose goal was to preserve as much tissue and bone as possible made a huge difference.”
While there’s a lot to learn from the Chicago Archaeopteryx, in this paper, O’Connor and her team focused on a few areas in particular: the head, the hands and feet, and the wing feathers.
“The bones in the roof of the mouth help us learn about the evolution of something called cranial kinesis— a feature in modern birds that lets the beak move independently from the braincase. That might not sound exciting, but to people who study bird evolution, it’s really important, because it’s been hypothesized that being able to evolve specialized skulls for different ecological niches might have helped birds evolve into more than 11,000 species today,” says O’Connor. Meanwhile, soft tissues preserved in the Chicago Archaeopteryx’s hands and feet bolster ideas that Archaeopteryx spent a lot of its time walking on the ground and might even have been able to climb trees.
The Chicago Archaeopteryx's wing feathers factor into a long-standing scientific debate about the origins of flight in dinosaurs. “Archaeopteryx isn’t the first dinosaur to have feathers, or the first dinosaur to have ‘wings.’ But we think it’s the earliest known dinosaur that was able to use its feathers to fly,” says O’Connor. “This is actually my favorite part of the paper, the part that provides evidence that Archaeopteryx was using its feathered wings for flying.”
The key to Archaeopteryx’s flight might be a set of feathers never before seen in a member of its species: a long set of feathers on the upper arm, called tertials.
“Compared to most living birds, Archaeopteryx has a very long upper arm bone,” says O’Connor. “And if you’re trying to fly, having a long upper arm bone can create a gap between the long primary and secondary feathers of the wing and the rest of your body. If air passes through that gap, that disrupts the lift you’re generating, and you can’t fly.”
However, modern birds have evolved a solution to this problem: a shorter upper arm bones, and a set of tertial feathers to fill the gap between the bird’s body and the rest of its wing.
“Our specimen is the first Archaeopteryx that was preserved and prepared in such a way that we can see its long tertial feathers,” says O’Connor. “These feathers are missing in feathered dinosaurs that are closely related to birds but aren’t quite birds. Their wing feathers stop at the elbow. That tells us that these non-avian dinosaurs couldn’t fly, but Archaeopteryx could. This also adds to evidence that suggests dinosaurs evolved flight more than once—which I think is super exciting.”
O’Connor says that this initial study is just the beginning for the Chicago Archaeopteryx. “We're learning something exciting and new from just about every part of the body that we have preserved. And this paper is really just the tip of the iceberg,” she says.
This study was contributed to by Jingmai O’Connor, Alex Clark, Pei-Chen Kuo, Yosef Kiat, Matteo Fabbri, Akiko Shinya, Constance Van Beek, Jing Lu, Min Wang, and Han Hu.
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Journal
Nature
Article Title
Chicago Archaeopteryx informs on the early evolution of the avian bauplan
Article Publication Date
14-May-2025
Illustration showing Archaeopteryx in life, including its tertial feathers that would have helped it fly.
Credit
Michael Rothman
The Chicago Archaeopteryx
Credit
Photo by Delaney Drummond. (c) Field Museum
Field Museum fossil preparators Connie Van Beek (left) and Akiko Shinya (right) working on the Chicago Archaeopteryx.
Credit
Field Museum
