Oldest Rib-Driven Breathing Evidence in Permian Amniote Fossils

Paleontologists have uncovered two exceptionally preserved mummified specimens of the early reptile Captorhinus aguti in a cave system near Richards Spur, Oklahoma, providing the oldest direct evidence of rib-driven breathing in amniotes, the group that includes modern reptiles, birds, and mammals. Dating to between 289 million and 286 million years ago during the early Permian period, the fossils reveal a sophisticated respiratory system that marked a pivotal shift in vertebrate evolution toward life on land.

The specimens, roughly the size of a modern bearded dragon and less than a meter long, were preserved in fine clay and saturated with mineral-rich groundwater and crude oil, which halted decomposition and maintained delicate structures. Advanced imaging techniques, including neutron computed tomography and synchrotron infrared spectroscopy, exposed not only bones and a three-dimensional skin covering with scale patterns but also intact cartilage in the rib cage, shoulder girdle, and sternum, along with traces of original proteins. These proteins represent the earliest known remnants in any terrestrial vertebrate, predating previous examples by nearly 100 million years.