Scientists Discover Oldest Fossil of Reptile with Rib-Based Breathing

Researchers from the University of Toronto have recently made a remarkable discovery in the United States, uncovering a mummified fossil of a reptile that stands as the oldest known example of rib-based breathing in amniotes—four-legged vertebrates. This significant finding paves the way for a deeper understanding of the evolution of respiratory systems in animals.

The study conducted by the scientists describes a respiratory system that has astonished researchers with its preservation, found in a small lizard-like creature known as Captorhinus aguti, which lived during the early Permian period. This reptile was discovered in cave systems near Richards Spur, where unique conditions allowed the fossil to remain in a death pose, a rare phenomenon in paleontology.

The creature, measuring only a few centimeters in length, preserved not only its bones but also its skin, calcified cartilage, and remnants of proteins. These organic molecules were found to be nearly 100 million years older than the previous oldest sample discovered in a dinosaur, making this finding extraordinarily valuable for science.

Ethan Muni, a co-author of the study, remarked, "The discovery of protein remnants is exceptional, and it significantly expands our understanding of what is possible in terms of soft tissue preservation in the fossil record." This discovery not only supports theories regarding the evolution of respiratory systems but also raises new questions about how these tissues managed to survive over millions of years.

The researchers utilized neutron computer tomography to explore the internal structure of the stone and identified the scaly skin with a wrinkled texture that enveloped the body and neck of the animal. The team examined three samples of Captorhinus, enabling them to reconstruct the complete respiratory apparatus of early amniotes for the first time. Paleontologists were able to recognize a segmented cartilaginous sternum, sternal and intercostal ribs, as well as structures connecting the thoracic cavity to the shoulder girdle.

Professor Robert R. Rice, one of the study's authors, speculated, "We hypothesize that the system found in Captorhinus represents an ancestral state for the type of rib-based breathing present in modern reptiles, birds, and mammals." This discovery indicates that the evolution of respiratory systems in animals underwent significant changes that allowed them to adapt to various living conditions.

Prior to the evolution of this system, amphibians dominated with a strategy that relied primarily on skin breathing and the pumping of air through the mouth and throat. Later, with the development of rib-based aspiration breathing, the muscles between the ribs began to expand and contract the thoracic cavity, facilitating a much more powerful gas exchange. This new breathing mechanism enabled animals to inhale more oxygen and exhale more carbon dioxide, marking a crucial step in their evolution.

To date, the discovered fossils are housed at the Royal Ontario Museum in Toronto, where they continue to be studied. The results of this important research were published in the prestigious journal Nature, underscoring their significance for science.