Scientists have solved a decades-old mystery about why ancient tetrapods – amphibian-like creatures that lived more than 300 million years ago – are preserved at one of Earth’s most important fossil sites. Ireland apparently had their bones cooked after they died.
The Jarrow assemblage is one of Ireland’s most important fossil sites and preserves some of the oldest amphibians to live in terrestrial environments. These fossils are 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 it is now difficult to distinguish the details of the fossils. The cause of this weathering has baffled scientists, with explanations for this weathering generally being attributed to the acid that dissolved the bones when the animals were first buried. This is until now.
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. , to analyze the chemistry of the bones to find the causes of this alteration.
Dr Aodhán Ó Gogáin, from the Trinity School of Natural Sciences, is the lead author of the study. He said:
“Normally in fossil bones we see that the original internal structure is preserved. But when we examine the X-ray images of the Jarrow fossils, we find that no internal bone morphology has been preserved and the bones have been partially replaced by the surrounding charcoal. .”
The team also found apatite preserved in the bones. Dr. Gary O’Sullivan, co-author of the study, said:
“The chemistry of apatite crystals can tell us a lot about how it formed, whether it grew organically in the animal, whether it formed when the animal was buried or if other factors influenced its growth. Apatite is a major constituent of living bone. it is not surprising that we find some preserved in these bones.However, when we examine the chemistry of apatite in the Jarrow bones, we find that this apatite was formed by heated fluids within the Earth
By Dr. Aodhán Ó Gogáin added:
“We were also able to radiometrically date apatite, which shows that it formed at a time when all the continents of Earth were coming together and colliding to form the supercontinent Pangea. When these continents collided, they formed mountain belts with superheated underground fluids. It was these superheated fluids, which circulated throughout Ireland, that cooked and melted the bones of these fossils, causing the weathering we see today.
Dr Patrick Wyse Jackson of Trinity, another co-author, said:
“The Jarrow assemblage is of major scientific importance and is an important part of Ireland’s geoheritage. It’s great that the question of what changed the fossil bones of these animals has finally been answered.”
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Material provided by Trinity College Dublin. Note: Content may be edited for style and length.