Line drawings of horseshoe crab fossils and specimens. Credit: Paris Natural History Museum
Horseshoe crab fossils dating back more than 300 million years have been discovered in County Clare, in a notable first for Ireland.
The fossil, measuring just 2 centimeters in size, was identified as Euplupus danae, a species well known in Britain, Europe, Russia and North America.
This is the first record of this species in Ireland and the first new horseshoe crab fossil discovered in Ireland since the 1800s.
The fossil was discovered near Doolin and the Cliffs of Moher by Pierre Guériault, an arthropod fossil expert at the University of Lausanne in Switzerland. Dr Geliau discovered the petrified remains while conducting joint fieldwork with Dr Eamonn Doyle, a geologist at the Burren and Cliffs of Moher UNESCO Global Geopark.
Dr Gerriault said: “We were surprised to find this fossil after many hours of searching. We quickly realized that this was an important discovery and an important addition to the known fossil facies of rocks in County Clare and Ireland.”
Line drawings of horseshoe crab fossils and specimens. Credit: Paris Natural History Museum
Dr Doyle added: “I had previously found small horseshoe crab footprints preserved as trace fossils in the rocks here, so it was exciting to see an example of the actual animal that made them. This discovery highlights the benefits of collaboration with international colleagues.”
The Clair Shale layer, where the fossils were found, is a mudstone deposit formed in relatively deep ocean near the equator. It took 320 million years for the rocks to be transported to their current location on the west coast of County Clare.
The horseshoe crab is not actually a crab, but a representative of another type of arthropod, the xyphoslanth, which is closely related to scorpions and spiders, and may have been carried by offshore currents into the deep ocean, where it then died and was preserved as a fossil.
Most Carboniferous horseshoe crabs are found in very shallow water deposits. Modern horseshoe crabs land in their thousands on sandy beaches along the East Coast of the United States to spawn, excavate nests, and lay thousands of eggs. It is unclear whether ancient fossil forms exhibited similar behavior.
This specimen is held in the collection of the Geology Museum, Trinity College, Dublin.