The oldest breath: A 300-million-year-old mummy reveals the origins of how amniotes breathe
Harvard University
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289-million-year-old reptile Captorhinus in its death pose in a cave system. Oil seepages, hyper-mineralized water, fine clays in this cave made it an ideal environment for mummification and fossilization of soft tissues like skin, cartilage, and protein remnants.
view moreCredit: Artwork by Dr. Michael DeBraga
Every breath you take is an ancient inheritance. The rise and fall of your chest, the intercostal muscles pulling your ribs outward, the rush of air into your lungs — this mechanism is so familiar it barely registers as remarkable. But a tiny, mummified reptile that died in an Oklahoma cave roughly 289 million years ago has revealed the oldest example of this breathing system in amniotes – a group that includes all reptiles, birds, mammals, and their common ancestors, among the first to conquer life on land.
In a new study published in Nature, researchers describe the extraordinary preservation of the oldest known costal breathing system in Captorhinus aguti, a small, lizard-like creature from the early Permian period. The mummified fossil, which is only a few inches long, preserves not only bones, but also three-dimensional skin, calcified cartilage, and — most astonishingly —protein remnants that predate the previous oldest-known example by nearly 100 million years.
“Captorhinus is an interesting lizard-looking critter that is critical to understanding early amniote evolution,” said Ethan Mooney, who co-led the study while a student at the University of Toronto in co-author Professor Robert R. Reisz’s lab and is now a PhD candidate in the Department of Organismic and Evolutionary Biology at Harvard University where he works with paleontologist Professor Stephanie Pierce. These creatures, which ranged in size from five centimeters to a few feet, were among the earliest known reptiles to experiment with living on land. During their time, they were thriving and numerous.
Captorhinus was discovered in the unique cave systems near Richards Spur, Oklahoma, a site so rich in late Paleozoic life that it holds the most diverse terrestrial vertebrate assemblage known from that era – a time already famous for producing the most species-rich terrestrial vertebrates. The site’s unique conditions, including oil-seep hydrocarbons and oxygen-free mud, preserved not only the animal’s bones, but also its skin and cartilage, resulting in a three dimensional mummified fossil frozen in its death pose, with its arm tucked beneath its body.
Using neutron computed tomography (nCT) at a specialized facility in Australia, the team was able to peer beneath the rock without disturbing the fossil. What Mooney found while processing the scans stunned him. “I started to see all these structures wrapped around the bones,” he said, “they were very thin and textured. And lo and behold, there was a nice wrapping of skin around the torso of this animal. The scaly skin has this wonderful accordion-like texture, with these concentric bands covering much of the body from the torso and up to the neck.” The pattern resembles the scales of modern worm lizards — small, burrowing reptiles alive today.
But the skin was only part of the story. The team studied three Captorhinus specimens from Richards Spur that, together, told a story about breathing. In one specimen, they identified a segmented cartilaginous sternum, sternal ribs, intermediate ribs, and structures connecting the ribcage to the shoulder girdle. For the first time in the fossil record, it was possible to view these structures in an early reptile and reconstruct the complete breathing apparatus of an early amniote.
Before amniotes evolved this system, the dominant strategy belonged to amphibians — breathing through their skin and pumping air through their lungs using their mouths and throats; strategies that modern amphibians still largely rely on today, but aren’t well suited for the more active lifestyles of amniotes. Costal aspiration breathing, in which the muscles between the ribs expand and compress the chest cavity to draw air deep into the lungs, is far more powerful, bringing more oxygen in and more carbon dioxide out.
“We propose that the system found in Captorhinus represents the ancestral condition for the kind of rib assisted respiration present in living reptiles, birds, and mammals” said Reisz.
Using ribcage musculature was an evolutionary innovation fundamental to the conquest of the terrestrial realm by these earliest ancestors of modern reptiles and mammals. This system likely also contributed to the explosive diversification of early amniotes, setting the stage for their dominance on land.
“It was a game changer that allowed these animals to adopt a much more active lifestyle,” said Mooney.
The find also revealed an unexpected bonus. Chemical analysis using synchrotron infrared spectroscopy detected remnants of original proteins preserved in the bone, cartilage, and skin. These organic molecules, never before seen in fossils from the Paleozoic era, are nearly 100 million years older than the previous oldest example, which was found in a dinosaur. “The protein remnant finding is exceptional,” Mooney said, “it dramatically pushes our understanding of what is possible in terms of soft tissue preservation in the fossil record.”
The fossils are now housed in the Royal Ontario Museum in Toronto, where they are available for future study. Meanwhile, Mooney has brought his expertise in early reptiles to Harvard, where he continues to explore the evolutionary mysteries of early reptiles, advancing our understanding of how these creatures helped shape the world we live in today.
llustrated whole body skeletal diagram in left side view depicting the cartilaginous components in yellow that are described for the first time in this study.
Credit
Reisz et al. (Nature 2026) diagram altered from Heaton & Reisz (1980). Heaton, M. J. & Reisz, R. R. A skeletal reconstruction of the early Permian captorhinid reptile Eocaptorhinus laticeps (Williston). J. Paleontol. 54, 136-143 (1980).
a) photo of the specimen encased in rock; b) nCT digital rendering showing the skeleton and cartilages including sternum and sternal ribs; c) illustrated diagram of Captorhinus aguti. Arrow points towards where the head would be.
Credit
Reisz et al. (Nature 2026) diagram altered from Heaton & Reisz (1980). Heaton, M. J. & Reisz, R. R. A skeletal reconstruction of the early Permian captorhinid reptile Eocaptorhinus laticeps (Williston). J. Paleontol. 54, 136-143 (1980).
Journal
Nature
Article Title
Mummified early Permian reptile reveals ancient amniote breathing apparatus
Article Publication Date
8-Apr-2026
Breathing and moving in the ancient world of reptiles: What a mummified 289-million-year-old reptile can reveal about us today
University of Toronto
image:
From a to d, showing outer skin, showing the corneous bands in the skin, the segmented skeleton with cartilages, and reconstructed parts of skeleton in colour showing the preserved parts of the rib cage and shoulder region.
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Credit: Robert Reisz
A 289-million-year-old mummified reptile is providing scientists with a window into how bodies have evolved when it comes to breathing and movement. Published in Nature on April 8, 2026, the study introduces the oldest known mummified remains of a terrestrial vertebrate — a small early Permian reptile called Captorhinus — preserved with its skin, native proteins, and the cartilage framework of its entire respiratory system still intact. The finding predates previous evidence of preserved biological proteins in fossils by nearly 100 million years.
“This is an exciting discovery in paleontology with great evolutionary significance,” says University of Toronto Mississauga researcher and lead author Robert Reisz. “This unprecedented preservation of a respiratory system showcases the oldest known complete rib cage for muscle powered inhalation and exhalation.”
The mummified reptile was likely preserved because it died in a cave system, became encased in fine clay, and was saturated with hydrocarbons from an oil seep, a rare combination that protected delicate soft tissues across geological time. Because the remains were very fragile, the research team skipped traditional fossil preparation techniques entirely and co-authors Joseph Bevitt and Ethan Mooney used neutron computed tomography (CT) scanning and imaging, and researchers from three different centers used geochemical techniques — including X-ray fluorescence (XRF), electron probe microanalysis (EPMA), and synchrotron radiation Fourier-transform infrared spectroscopy (SR-FTIR) — to image and analyze the specimens. Co-author Tea Maho from the University of Toronto Mississauga also conducted histological sampling that indicated the cartilages are calcified as in living lizards, and the chemical analyses confirmed this interpretation.
“We propose that this system found in Captorhinus represents the ancestral condition for the kind of rib-assisted respiration present in living reptiles, birds, and mammals. This efficient respiratory apparatus is important for their more active, energetic, and competitive lifestyles compared to their amphibian counterparts,” said Reisz.
Equally striking is evidence that the shoulder girdle shows that there was likely movement on each side during locomotion, a feature seen in many living lizards and now confirmed as an ancient trait rather than a later evolutionary innovation.
“The mummified Captorhinus is among the most significant early amniote fossils in the world,” added Mooney. “It has offered an unparalleled window into the appearance, lifestyles, and evolution of the earliest reptiles, expanding dramatically our understanding of this pivotal episode of amniote evolution. As more work continues on this time period, more incredible discoveries are sure to be unearthed.”
Journal
Nature
Subject of Research
Animals
Article Title
Mummified early Permian reptile reveals ancient amniote breathing apparatus
Article Publication Date
8-Apr-2026
Image of a fossil.
Image of a fossil.
Credit
Ethan Mooney
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