Scientists have solved a decades-old mystery about why ancient tetrapods – amphibian-like creatures that lived 300 million years ago – are preserved in one of the most important fossil sites on Earth.
The Jarrow assemblage is one of the most important fossil sites in Ireland and preserves some of the oldest amphibians to live in terrestrial environments. These fossils were found in a coal seam in County Kilkenny.
The fossils from this site have a unique characteristic: their original internal bone morphology has been altered so that the details of the fossils are now difficult to distinguish. The cause of this weathering has puzzled scientists, and explanations for this weathering are usually due to the acid that dissolved the bones when the animals were buried. This is so far.
A team of scientists from Trinity College Dublin, University College Dublin, National University of Ireland, Galway, University of Birmingham and the Gemological Institute of America used a combination of CT scans to produce X-ray images of the fossil and laser ablation. , analyze the bone chemistry to find the reasons for this change.
Lead author of the study is Dr Aadhan O’Gaughan from Trinity School of Natural Sciences. He said:
“Usually in fossil bones we see the original internal structure preserved. But when we examined the X-ray images of the jaro fossils, we found that the internal bone morphology was not preserved and was partially replaced by charcoal around the bones. . »
The team also found apatite preserved in the bones. Study co-author Dr. Gary O’Sullivan said:
“The chemistry of the apatite crystals can tell a lot about how it formed, whether it grew organically in the animal, formed when the animal was buried, or whether other factors influenced its growth. Apatite is the main component of living bone. It is not surprising that some of these bones are preserved. However, when we examined the chemistry of the apatite in the jaro bones, we found that this apatite was formed by heated fluids inside the Earth.
Dr. Aodhán Ó Gogáin added:
“We were also able to radiometrically quantify the apatite, which shows that it formed when all of Earth’s continents came together and collided to form a supercontinent. When these continents collided, they formed superheated mountain ranges using subterranean fluids. It was these superheated fluids that spread across Ireland that cooked and melted the bones of these fossils, giving rise to the climate we see today.
Dr Patrick Wise Jackson of Trinity, another co-author, said:
“The Jarrow assemblage is of great scientific importance and an important part of Ireland’s geoheritage. It is nice to finally have an answer to the question of what changed the fossil bones of these animals. »
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