Dr Joseph Bevitt and Prof Robert Reisz examine a specimen from the same cave where Captorhinus was found. The sample was positioned for imaging using neutron tomography at ANSTO. Picture ANSTO

In a breakthrough for international science, experts at ANSTO's Lucas Heights campus have used advanced nuclear imaging to unlock the secrets of the world's oldest mummified land vertebrate.

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Using the capabilities of neutron imaging, ANSTO scientists helped visualise the exceptionally delicate soft tissues of Captorhinus, a small reptile preserved in limestone for nearly 300 million years.

This non-destructive technique allowed the research team to see through solid rock to identify skin, cartilage, and even protein remnants without damaging the fragile 289-million-year-old specimen.

The study, recently published in the journal Nature, marks a major milestone in understanding how prehistoric life transitioned to a permanent existence on land.

Dr Joseph Bevitt, manager of an instrument group at the Australian Centre for Neutron Scattering, performed the imaging that revealed the animal's internal anatomy in unprecedented detail. Because the remains were so fragile, traditional mechanical or chemical cleaning methods were impossible; only the "Dingo" neutron tomography instrument at ANSTO possessed the ability to peer inside the limestone while keeping the fossil intact.

What the team discovered was a biological time capsule. The reptile was found in a death position, encased in fine clay and saturated with oil-seep hydrocarbons within an ancient cave system. This specific environment preserved the oldest known complete rib cage designed for muscle-powered inhalation and exhalation.

The world's oldest land fossil's soft tissue was seen for the first time. Picture ANSTO

This discovery provides the missing link in evolutionary history, showing how early vertebrates moved away from the gulping breath of amphibians toward the efficient, rib-assisted breathing used by modern reptiles, birds, and mammals today.

The imaging also revealed evidence of pectoral girdle mobility. This suggests that Captorhinus possessed the ability to move its shoulders independently of its ribs while walking - a trait that humans and crocodiles alike take for granted, but which was a radical adaptation for life on land 300 million years ago.

Lead author Professor Robert Reisz said these findings are of immense evolutionary significance, representing the ancestral blueprint for the active and energetic lifestyles of modern land animals.

This was a global collaboration involving Harvard University, the University of Toronto, and institutions from Taiwan and China, and highlights how world-leading nuclear science facilities such as the one at ANSTO are at the centre of international discovery.

For those interested in seeing this piece of history first hand, a Captorhinus fossil is on display at ANSTO, where visitors can view the ancient reptile during an onsite tour and learn more about the technology.