A group of sea urchins which died together on the seafloor almost 350 million years ago have been found in fossilised form at Hook Head, Co Wexford, by a team of scientists.
"Experts from University of Galway’s school of natural scientists led the team which recorded the fine, described as “one of the most important in Irish palaeontology in recent times”.
Sea urchins, or echinoids, are a group of marine animals, related to starfish, the scientists explain.
They have globular plated bodies covered by numerous defensive spines, which fall away after the urchin dies.
The scientists say that over 200 complete fossil echinoids are preserved in exquisite detail on a limestone surface, in an area of just one square metre.
Detailed view of fossil sea urchins, with their spines still attached, preserved on limestone surface at Hook Head, Wexford (2 Euro coin for scale). Photo: courtesy of the Royal Irish Academy
“All of the Hook Head specimens have their spines still attached, and they apparently died together on the seafloor almost 350 million years ago - a dramatic moment now frozen in time on the rock surface on the coast of south-east Ireland,” they say.
“The limestone layer containing the fossil urchins was in danger of being lost to coastal erosion, so the scientific team mounted a rescue operation to save it,” they state.
Lead author in the study, palaeontologist Dr Nidia Álvarez-Armada, said she initially discovered the fossil sea urchins on a rocky coastal outcrop when surveying the geology of Hook Head peninsula for her undergraduate Bachelor of Science thesis at University of Galway.
“ When I first noticed the echinoids on the limestone surface, I was completely astonished by both the sheer number of fossil specimens present and also their exceptional preservation,” she said.
“The significance of the find was instantly apparent, and I immediately began mapping and recording the shape, size and position of each individual urchin on the rock surface,” she said.
“ This work took several weeks to complete, but it was important to carefully document the fossil find in as much detail as possible.”
As the Hook Head is protected under law, approval for the recovery was granted by several State agencies and the local landowner.
Rescue and recovery of the limestone slab containing the fossil sea urchins at Hook Head, Wexford. Photos: Dr Sarah Gatley, Geological Survey Ireland
Following successful removal, the team said it “immediately entrusted the fossil-bearing slab to the National Museum of Ireland for conservation and further study”.
The discovery and recovery of the hundreds of fossil sea urchins were recently reported in the Irish Journal of Earth Sciences, published by the Royal Irish Academy.
The Hook Head fossil find is said to have the potential to reveal important information about the nature of seafloor communities during the Carboniferous - a time period that occurred “long before dinosaurs ever walked on land, when the marine realm was very different to today”.
University of Galway school of natural scientists expert Dr John Murray, who co-authored the paper and supervised the original project, said that is “quite exceptional to find Carboniferous fossil sea urchins so perfectly preserved and in such large numbers like this”.
“In life, these particular echinoids had very flexible plated bodies, covered with many spines, which usually disarticulated and dispersed rapidly after death, leaving little trace of them behind,” he said.
“ The Hook Head urchins must have been buried quite quickly after they died, with little or no post-mortem disturbance; however, it remains unclear why they congregated in such large numbers at this location on that ancient seafloor,” he said.
“The significance of this discovery was such that all of the members of the rescue team willingly volunteered their time and expertise to travel to Hook Head to help salvage the fossil-bearing slab,”Dr Murray added.
“We consciously chose to leave this important fossil find in the care of the National Museum of Ireland immediately - I guess it was our way of giving this piece of priceless geoheritage back to the people of Ireland,” he said.
The full study in The Irish Journal of Earth Sciences can be read here
