Paleontologists have discovered remarkable specimens of early reptiles, specifically Captorinus aguti, dating back 289 million years. These preserved fossils showcase three-dimensional skin coverings, a complete shoulder girdle, rib cages including cartilage, and astonishingly, protein remains that are nearly 100 million years older than any previously known examples.
Captorinus aguti. Image credit: Michael Debraga.
The transition from aquatic to terrestrial life marked a key milestone in vertebrate evolution. Early amniotes required new breathing techniques to adapt to the dry environment.
Initially, these early amniotes relied mainly on throat and skin respiration, but as they evolved, later amniotes utilized their ribs and thorax for more efficient lung ventilation.
Due to the rarity of soft tissue fossilization, direct evidence of this evolutionary transition has been limited.
“Captorinus aguti is a notable lizard-like species that plays a crucial role in understanding the early development of amniotes,” stated Ethan Mooney, a doctoral candidate at Harvard University.
“Growing over five centimeters long, these reptiles were among the first to explore terrestrial habitats, exhibiting thriving populations at that time.”
Three exceptionally preserved Captorinus aguti specimens were discovered in a unique cave system near Richards Spur, Oklahoma, encased in fine clay and oil, which revealed unprecedented structural features.
In one specimen, researchers identified a segmented cartilaginous sternum, sternal ribs, intermediate ribs, and structures connecting the thorax to the shoulder girdle.
This discovery enabled scientists to reconstruct the complete respiratory apparatus for early amniotes for the first time in the fossil record.
Professor Robert R. Rice, a paleontologist at the University of Toronto and Jilin University, explained, “We propose that the respiratory system in Captorinus aguti represents an ancestral state of rib-assisted respiration recognized in modern reptiles, birds, and mammals.”
“The utilization of thoracic musculature marked an evolutionary innovation that facilitated the terrestrial conquest by the early ancestors of modern reptiles and mammals,” he added.
“This innovation likely spurred the rapid diversification of early amniotes, paving the way for their dominance on land.”
“Such adaptations enabled these creatures to lead a more active lifestyle,” Mooney concluded.
Employing synchrotron infrared spectroscopy, researchers also uncovered remnants of original proteins preserved in bones, cartilage, and skin. These organic molecules, unprecedented in Paleozoic fossils, are approximately 100 million years older than the oldest examples found in dinosaurs.
“The discovery of protein remnants is extraordinary,” remarked Mooney. “It significantly enhances our understanding of soft tissue preservation in the fossil record.”
This groundbreaking finding is detailed in a recent paper published in the journal Nature.
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R.R. Rice et al. Mummified Early Permian Reptiles Reveal Ancient Amniote Breathing Apparatus. Nature, published on April 8, 2026. doi: 10.1038/s41586-026-10307-y
Source: www.sci.news
