Researchers now know why ancient tetrapods, which resembled amphibians and lived more than 300 million years ago, appeared to have had their bones burned after passing away in one of Ireland’s most significant fossil sites.
One of Ireland’s most significant fossil sites, the Jarrow Assemblage, contains some of the earliest amphibians to have lived on land. In Co. Kilkenny, these fossils were discovered in a coal seam.
The interior bone morphology of the fossils from this site has been changed from their original state, making it impossible to discern fine details. Scientists are perplexed as to the reason for this transformation, which is typically attributed to acid dissolving the bones during the first burial of the animals. Up until now, that is.
In order to investigate the causes of this ancient tetrapods alteration, a team of scientists from Trinity College Dublin, University College Dublin, the National University of Ireland, Galway, the University of Birmingham, and the Gemological Institute of America combined computed tomography and laser ablation to produce X-ray images of the fossil and analyze the chemistry of the bones.
The study’s principal author is Dr. Aodhán Gogáin from Trinity’s School of Natural Sciences. He stated:
“In most fossilized bones, the internal original structure is still present.” However, we discovered that little internal bone morphology had been preserved when we viewed the X-ray photographs of the fossils from Jarrow and that the bones had been partially replaced by the coal in the environment.
Apatite preserved in the bones was also discovered by the team. Dr. Gary O’Sullivan, one of the study’s co-authors, stated,
The chemistry of the apatite crystals can reveal a lot about how they developed, including whether they developed naturally inside the animal, during burial, or as a result of other circumstances. It is hardly surprising that apatite, which makes up a significant portion of live bone, has been retained in these bones. However, we discover that the apatite in the bones from Jarrow was created by heated fluids within the Earth when we examine the chemistry of the apatite in those bones.
Dr. Aodhan Gogáin continued:
We have also been able to radiometrically date the apatite, which demonstrates that it developed at a time when the Earth’s continents were interacting and merging to form the supercontinent Pangaea. These continents produced mountain belts as they met, with superheated fluids streaming out of them. These extremely hot fluids, which permeated all of Ireland, cooked and melted the bones of these fossils, resulting in the modifications we see today.
Dr. Patrick Wyse Jackson, a co-author from Trinity, stated:
“The Jarrow assemblage is important to Ireland’s geohistory and has significant scientific significance.” It’s wonderful that the mystery of what changed the fossilized bones of these animals has now been answered.
