Rock cores archived at the Geological Survey of Ireland since early this century have yielded a treasure trove of ancient fossils, some of the best of their kind found anywhere in the world.
They are providing a remarkable look backwards in time that is teaching important lessons about evolution.
The cores were all taken near Castlecomer, Co Kilkenny, during a prospect for coal seams, explained Dr Patrick Orr of the Department of Geology at NUI Galway. It was known that the cores contained some fossils, he said. "They were first described about 70 years ago but the cores were probably drilled between 1908 and 1915."
They were identified in 1920 by Ms Mabel Wright, a biologist whose husband was thought to have worked at the survey. She identified about 25 specimens of an ancient crustacean, conchostracan branchiopods which were a type of arthropod and an early relative of shrimps and lobsters.
Dr Orr came across a reference to Ms Wright's findings and some original drawings while searching through a 1969 bibliography of research and immediately contacted Prof Derek Briggs of the University of Bristol, a world expert on these arthropods. The two got funding and agreed to study the cores in a collaboration which over time involved Dr Stuart Kearnes of Bristol and Dr Matthew Parkes and Dr Andy Sleeman of the Geological Survey.
Dr Orr went to the survey and started to examine the cores. These were already cut into discs but they were given permission to further subdivide them to expose more of their hidden contents, and as they searched they found more and more fossils. They now have more than 200 specimens collected from two different bore hole locations near Castlecomer.
The sedimentary rocks in which they were recovered date back 315 million years, Dr Orr said, "one of the younger [rock] series" in Ireland which typically were formed between 300 million and 540 million years ago. The Ardra bore hole was about 830 feet deep and the Hollypark cores were about 450 feet deep. The creatures when alive were less than half an inch across and were like a small shrimp encased in a two halved shell or "carapace", not hard like a seashell but a soft living shell like a thinner version of a lobster's body.
The Irish fossils are amazingly well preserved, he said. "The sheer scale of the preservation in terms of what we can pick out is remarkable."
Usually only the "hard parts" of a creature such as bone or teeth survive as fossils, but under exceptional conditions the more decay-prone "soft parts" such as muscle and internal organs are preserved. This gives palaeontologists a more complete picture of a creature's anatomy.
Surprisingly, "virtually identical" creatures still populate the world's waterways. "Living examples occur today in fresh water environments over almost all the globe, although not in Britain or Ireland," Dr Orr explained.
Their ability to survive over such a long period without significant evolutionary change was a puzzle, he said. "One argument suggests it is tied up with the fact that they can survive in a very hostile environment." They can tolerate severe drought and near complete dessication but immediately revive when water again becomes available.
