Mummified 289-million-year-old reptile reveals earliest evolution of rib-powered breathing on land

A 289-million-year-old Captorhinus fossil reveals the origin of rib-powered breathing. Harvard researchers find oldest protein traces ever recorded.

By: AXL Media

Published: Apr 23, 2026, 8:26 AM EDT

Source: Information for this report was sourced from Harvard University

A Biological Blueprint for Modern Respiration

The fundamental mechanism of human breathing has been traced back nearly 290 million years following the discovery of a mummified reptile in the Richards Spur cave system. According to a study published in Nature, the small lizard-like creature known as Captorhinus aguti provides the earliest known evidence of the rib-powered breathing system shared by modern mammals, birds, and reptiles. While the specimen is only a few inches long, its preservation is so exceptional that it contains far more than skeletal remains, offering a detailed look at the soft tissues that enabled early vertebrates to move beyond the limitations of amphibian life.

Extraordinary Preservation in the Richards Spur Caves

The fossil was unearthed in Oklahoma, where unique environmental conditions allowed for a rare form of three dimensional mummification. Oil seep hydrocarbons and oxygen-free mud acted as a natural preservative, protecting delicate cartilage, skin, and even protein remnants from decay. According to Ethan Mooney, a PhD candidate at Harvard University who co-led the study, the specimen was found in its final death pose with one arm tucked beneath its body. This site is renowned for containing the most diverse collection of terrestrial vertebrates from the early Permian period, yet this specific find stands out for its unprecedented level of anatomical detail.

Scanning the Layers of Prehistoric Skin

To examine the specimen without compromising its integrity, researchers utilized neutron computed tomography in Australia to peer through the rock. The resulting scans revealed a textured wrapping of scaly skin covering the animal's torso and neck. The skin exhibits a distinct accordion-like pattern of concentric bands, which Mooney noted bears a striking resemblance to the scales of modern burrowing worm lizards. This discovery marks a significant milestone in paleontology, as it allows scientists to visualize the external appearance and structural wrapping of an animal that lived long before the rise of the dinosaurs.