Objective:

To investigate the evolutionary transition from buccal pumping and cutaneous respiration to rib-powered ventilation in amniotes using a well-preserved fossil, highlighting its significance in understanding vertebrate evolution.

Key Findings:

• Captorhinus aguti exhibits the oldest known amniote breathing apparatus with an articulated ribcage and shoulder girdle.
• The fossil preserves three-dimensional skin, calcified cartilage, and protein remnants, including the oldest known protein in a terrestrial vertebrate.
• The ribcage and shoulder girdle form an integrated thoracic skeleton similar to that of modern reptiles, indicating capability for costal aspiration breathing, alongside previously undescribed structures such as a cartilaginous sternum.

Interpretation:

The findings suggest that Captorhinus represents an ancestral condition for rib-assisted respiration in modern reptiles, birds, and mammals, marking a significant adaptation for terrestrial life and enabling more active lifestyles.

Limitations:

• The study is based on a single fossil specimen, which may limit the generalizability of the findings, especially given the rarity of such well-preserved fossils.
• Further research is needed to explore the prevalence of similar thoracic structures in other early amniotes.

Conclusion:

The discovery of Captorhinus aguti enhances understanding of the evolution of breathing mechanisms in amniotes and suggests potential for further discoveries in similarly preserved fossils, paving the way for future research on early amniote adaptations.