Captorhinus was used
Rib-assisted breathing would have allowed the first amniotes a more active life on land, favoring their evolutionary diversification. “Mummy” of a 289-million-year-old reptile helps explain everything in a new study.
A small reptile, which lived in a cave 289 million years ago, is actually much more than bones today. The fossil also has three-dimensional skin, calcified cartilage and traces of protein. And don’t forget, of course, the fact that it is helping us unravel the origin of one of the most important respiratory systems in the evolution of terrestrial vertebrates — the same principle that allows breathing today in reptiles, birds and mammals, including humans.
Found in present-day Oklahoma, in the United States, the Captorhinus was used lived at the beginning of the Permian period. According to researchers, its protein remains are almost 100 million years older than any previously identified in fossils.
A study in Nature on April 8 describes the importance of this animal for understanding the evolution of amniotasthe group that includes reptiles, birds, mammals and their common ancestors. They were among the first vertebrates to fully adapt to life on dry land.
The fossil was found at the Richards Spur paleontological site in Oklahoma, an area known for exceptional preservation of late Paleozoic land vertebrates. The caves’ unusual conditions—including the presence of hydrocarbons from oil seeps and oxygen-depleted mud—helped preserve soft tissue like skin and cartilage. The specimen remained in three dimensions, almost like a mummy, compared to , with one of the legs folded under the body.
To study the fossil without damaging it, the team turned to neutron computed tomography. The images revealed fine, textured structures around the bones, including skin with a fold-like pattern that the researchers compared to that of some modern-day burrowing reptiles.
The most relevant discovery, as the title of this article predicts, is linked to breathing. The analysis of three specimens of Captorhinus allowed the reconstruction of a respiratory system based on the rib cage, with a segmented cartilaginous sternum, sternal ribs and connections to the shoulder girdle. This mechanism, known as costal suction breathinguses the muscles between the ribs to expand and compress the chest cavity, allowing air to enter the lungs.
Before this innovation, many amphibians depended mainly on their skin and mouth to breathe, a less efficient system that limited physical activity. Breathing assisted by the ribs would have allowed the first amniotes a more active life on land, favoring their evolutionary diversification.
The specimens are now at the Royal Ontario Museum, in Toronto, Canada, where they will continue to be available for research.
