Analysis: cousins of the common woodlice were crawling around on Irish land as long as 360 million years ago

A quarry in Co Kilkenny is shaping the understanding of what roamed our planet millions of years ago. In 1908, a fossil was discovered in a quarry at Kiltorcan, Co Kilkenny. The site has been internationally known since the mid 19th-century as the location of a number of plant, freshwater bivalve, fish and crustacean fossils.

The Kiltorcan quarry is about 400 million years old and has been internationally known for its rich assemblage of fossil ferns since 1853. It provides a remarkable snapshot of life at the end of the Devonian period (360 million years ago) when significant evolution amongst Earth’s plants was taking place and is a very exciting site for scientists across the world.

Our research re-examined the fossil found in 1908 and we now have a deeper understanding of what lived on our planet at drastically different periods. This was a time when the Earth's atmosphere was very different with higher temperature and C02 concentrations.

3-D rendering of oxyuropoda obtained using digital microscopy. Image: Ninon Robin

We wanted to see what species lived so we used state-of-the-art modern imaging technology to create a new picture of the Oxyuropoda, a land-based creature larger than the modern woodlice. We were able to establish that old cousins of the common woodlice were crawling on Irish land as long as 360 million years ago.

Woodlice and their relatives form a group of crustaceans named peracarids that are as species-rich as the more famous group comprising krill, crabs and shrimps named eucarids. From their ancestral marine habitat, some peracarids have, unlike eucarids, evolved fully terrestrial ground-crawling ecologies, inhabiting even commonly our gardens, for example pillbugs and sowbugs, which are very common in Ireland.

Using new modern imaging techniques, we determined that Oxyuropoda was actually a peracarid crustacean, even the oldest known one. This supports the theory that woodlice cousins were already crawling on Irish lands at that very early time, 360 million years ago.

From previous genomic and molecular studies, scientists had suggested that this group of crustaceans must have appeared around 450 million years ago. However their fossils were very rare in the Paleozoic era, which was 560-250 million years ago, so we had no idea at all how they looked at that time, nor if they were marine or yet terrestrial.

Our work advances science’s understanding of when land-dwelling species of crustaceans roamed the earth, and what they looked like.

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