An international research team has identified the oldest known mummified remains of a terrestrial vertebrate, a 289-million-year-old reptile named Captorhinus.
Published in Nature, the findings offer insights into early reptile biology and the evolution of respiratory systems in land vertebrates.
The exceptionally well-preserved specimen, which includes soft tissues, allowed for the reconstruction of ancient biological structures.
Discovery and Preservation
The Captorhinus remains were found in a death position and included a complete covering of skin, native protein remnants, and cartilage forming the respiratory system's skeleton. Researchers propose that the extraordinary preservation of these delicate tissues resulted from the specimen's encasement in fine clay and saturation with oil-seep hydrocarbons within a cave system. The discovery of endogenous protein remnants in the specimen predates previous evidence of such preservation by nearly 100 million years.
Dr. Joseph Bevitt from the Australian Centre for Neutron Scattering (ANSTO) utilized neutron imaging to obtain detailed information about the animal’s internal structures, including skin, bone, and cartilage. This technique was crucial for visualizing delicate internal organs preserved within limestone rock without causing damage, as traditional mechanical or chemical preparation methods were avoided due to the specimen's fragility.
Evolutionary Insights
According to lead author Professor Robert Reisz, these discoveries enabled the reconstruction of important aspects of this early reptile's biology, holding significant evolutionary implications. Key findings include:
- The preservation of cartilaginous components of the amniote respiratory system, representing the oldest known complete rib cage adapted for muscle-powered inhalation and exhalation.
- Evidence of pectoral girdle mobility, indicating the ability of the animal to move its shoulders relative to its ribs during locomotion.
Vertebrates began walking on land between 390 and 365 million years ago. While much is understood about the evolution of fins into limbs, less is known about the anatomical evolution supporting muscle-powered air breathing on land. The respiratory system identified in Captorhinus is proposed to represent the ancestral condition for rib-assisted respiration observed in living reptiles, birds, and mammals.
This efficient respiratory apparatus is considered important for supporting the more active lifestyles of these animals compared to amphibians.
Research Collaboration
The research involved an international collaboration between a University of Toronto team and collaborators from Harvard University (US), the National Synchrotron Radiation Research Center (Taiwan), and Jilin University (China).