Full Breakdown
Fossil of Early Permian Reptile Reveals First Rib-Based Breathing System and Ancient Protein Traces
4/25/2026, 2:33:15 PM
Groundbreaking Discovery of Early Amniote Breathing System
A three-dimensional fossil of the early Permian reptile *Captorhinus aguti* was recovered from cave deposits near Richards Spur, Oklahoma. Dated to ~289 million years ago, the specimen preserves bone, skin, calcified cartilage, and molecular remnants, offering an unprecedented view of early amniote anatomy.
Context: Early Amniotes and Richards Spur
*Captorhinus* belongs to amniotes, the lineage that gave rise to reptiles, birds, and mammals. Richards Spur is famed for a diverse late Paleozoic vertebrate assemblage, whose preservation owes to oil-seep hydrocarbons and anoxic mud that inhibited decay of soft tissues.
Researchers and Institutions
The study was led by Ethan Mooney (University of Toronto student, now Harvard PhD candidate) with Professor Robert R. Reisz and paleontologist Stephanie Pierce. Neutron computed tomography was performed in Australia; the fossils are housed at the Royal Ontario Museum.
Anatomical Insights: Rib-Based Costal Aspiration
Three specimens show a segmented cartilaginous sternum, sternal and intermediate ribs, and muscular links to the shoulder girdle. These features demonstrate costal aspiration breathing, where intercostal muscles expand the chest to draw air, representing the earliest rib-based respiration in amniotes.
Molecular Findings: Ancient Protein Remnants
Synchrotron infrared spectroscopy detected original protein traces in bone, cartilage, and skin. These proteins are nearly 100 million years older than any previously reported, extending the known temporal range of molecular preservation.
Official Statements & Responses
Mooney called the fossil “critical to understanding early amniote evolution” and a “game changer” for terrestrial activity. Reisz said the breathing system likely reflects the ancestral condition for rib-assisted respiration in modern reptiles, birds, and mammals. Both noted the protein discovery expands expectations for soft-tissue preservation.
Verbatim Quotes
- “Captorhinus is an interesting lizard-looking critter that is critical to understanding early amniote evolution,” — Ethan Mooney, co-lead author
- “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” — Robert R. Reisz, professor
- “It was a game changer that allowed these animals to adopt a much more active lifestyle,” — Ethan Mooney, co-lead author
- “it dramatically pushes our understanding of what is possible in terms of soft tissue preservation in the fossil record.” — Ethan Mooney, co-lead author
Implications for Evolutionary Biology
The rib-based breathing system likely enabled higher metabolic rates and greater locomotor ability, facilitating early amniote diversification on land. The protein evidence expands the toolkit for paleobiology, showing that molecular data can survive far longer than previously recognized.
What’s Next
The *Captorhinus* specimens remain at the Royal Ontario Museum for further study. Mooney’s team at Harvard plans to search for additional early amniote fossils and apply advanced imaging and molecular analyses to deepen understanding of vertebrate respiration origins.
