Every breath you take is part of a very old story. The steady movement of your chest, the outward pull of the muscles between your ribs, the air filling your lungs feels completely normal. But this familiar process goes back hundreds of millions of years. A beautifully preserved reptile that died in an Oklahoma cave some 289 million years ago has revealed the earliest known example of this breathing system in amniotes. Amniotes, a group that includes reptiles, birds, mammals, and their common ancestors, were among the first animals fully adapted to life on land.
In a study published in the journal Nature, scientists captorinus was used Early Permian. Although only a few inches long, this fossil contains much more than bone. It preserves three-dimensional skin, calcified cartilage, and even trace amounts of protein. These protein remains are nearly 100 million years older than any fossils identified so far.
”captorinus “This is an interesting lizard-like creature that is important for understanding the early evolution of amniotes,” said Ethan Mooney, who co-led the study while a student in co-author Professor Robert R. Rice’s lab at the University of Toronto and is now a doctoral candidate in Harvard’s Department of Organic and Evolutionary Biology, collaborating with paleontologist Professor Stephanie Pearce. They grew to several feet and were one of the first animals to explore life on land, making them widespread and successful at the time.
Richards Spar’s precious treasures
The fossil was discovered in a cave system near Richards Spur, Oklahoma, known for its incredible record of late Paleozoic life. The site already contains the most diverse collection of terrestrial vertebrates of its time. Unique environmental conditions helped preserve the ruins. The hydrocarbon and oxygen-free mud that the oil oozed out protected not only bones but also delicate tissues such as skin and cartilage.
The resulting specimen looked like a three-dimensional mummified fossil, frozen in its final position with one arm tucked under the body. This level of preservation is extremely rare and provides an extremely detailed view of ancient anatomy.
High-tech scan reveals skin and structure
The researchers used neutron computed tomography (nCT) at a specialized facility in Australia to examine the fossils without damaging them. The scans allowed us to look beneath the rock and reveal details hidden inside.
What Mooney observed during his analysis was unexpected. “You started to see all these structures wrapped around the bones. They were very thin and textured, and lo and behold, this animal had skin wonderfully wrapped around its torso. The scaly skin had a wonderful accordion-like texture, and these concentric bands covered most of the body from the torso to the neck,” he said. This pattern closely resembles the scales found in modern-day earthworm lizards, small burrowing reptiles that still live today.
First rib-based breathing system reconstruction
The preserved skin is only part of the discovery. By studying three things captorinus Using specimens taken from Richards Spur, researchers were able to piece together how the animal breathes. One fossil revealed a segmented cartilaginous sternum, along with the sternal ribs, middle ribs, and connections between the thorax and shoulder girdle.
For the first time, scientists clearly observed these structures in early reptiles and were able to reconstruct a complete respiratory system in early amniotes. This provided direct evidence of rib suction breathing, in which the intercostal muscles expand and compress the thoracic cavity to draw air into the lungs.
Before this system evolved, amphibians relied on a different method. They breathe through their skin, using mouth and throat movements to force air into their lungs. This approach is still effective for many amphibians, but it limits activity levels. Rib-based breathing allows for deeper, more efficient airflow, bringing in more oxygen and removing carbon dioxide more effectively.
“We propose the following system. captorinus “This represents an ancestral state of rib-assisted breathing that exists in modern reptiles, birds, and mammals,” Rice said.
Key innovations for life on land
Using the muscles of the rib cage for breathing was a major evolutionary step. This may have allowed early amniotes to maintain a more active lifestyle, which may have helped them spread and diversify across terrestrial environments.
“This was an innovation that allowed these animals to adopt a more active lifestyle,” Mooney said.
This innovation played a major role in the success of reptiles and their descendants and may have laid the foundation for their dominance in terrestrial ecosystems.
Ancient proteins push the boundaries of science
This discovery also included some surprising discoveries. The researchers used synchrotron infrared spectroscopy to detect traces of the original proteins preserved within the fossil bones, cartilage, and skin. These molecules are the oldest of their kind ever identified, predating previous examples found in dinosaur fossils by almost 100 million years.
Professor Mooney said: “The discovery of protein remains is exceptional and dramatically advances our understanding of what is possible in terms of preserving soft tissues in the fossil record.”
A window into early evolution
The fossil is currently housed at the Royal Ontario Museum in Toronto, where it will continue to be studied. Mooney has since continued his research at Harvard University, focusing on early reptiles and their evolutionary history.
Such discoveries provide a clearer picture of how early vertebrates adapted to life on land and how key innovations such as efficient breathing helped shape the course of evolution.
