It’s not every day that a new discovery sheds light on a world that existed millions of years ago. But that’s precisely what happened when the largest-ever fossil of a giant millipede was found on a beach in the north of England. This millipede was as big as a car and roamed the earth during the Carboniferous Period, which was over 100 million years before the Age of Dinosaurs.
The fossil, which is the remains of a creature called Arthropleura, dates back about 326 million years ago. The discovery has revealed that Arthropleura was the largest-known invertebrate animal of all time, larger than the ancient sea scorpions that were the previous record holders.
The fossil was discovered in January 2018 in a large block of sandstone that had fallen from a cliff to the beach at Howick Bay in Northumberland. “It was a complete fluke of a discovery,” said Dr. Neil Davies from Cambridge’s Department of Earth Sciences, the paper’s lead author. “The way the boulder had fallen, it had cracked open and perfectly exposed the fossil, which one of our former Ph.D. students happened to spot when walking by.”
The fossil is just the third such fossil ever found and is also the oldest and largest. The segment is about 75 centimeters long, while the original creature is estimated to have measured around 2.7 meters long and weighed around 50 kilograms. The results are reported in the Journal of the Geological Society.
The specimen, which is made up of multiple articulated exoskeleton segments, is broadly similar in form to modern millipedes. Unlike the cool and wet weather associated with the region today, Northumberland had a more tropical climate in the Carboniferous Period when Great Britain lay near the Equator. Invertebrates and early amphibians lived off the scattered vegetation around a series of creeks and rivers. The specimen identified by the researchers was found in a fossilized river channel. It was likely a molted segment of the Arthropleura’s exoskeleton that filled with sand, preserving it for hundreds of millions of years.
The fossil was extracted in May 2018 with permission from Natural England and the landowners, the Howick Estate. “It was an incredibly exciting find, but the fossil is so large it took four of us to carry it up the cliff face,” said Davies.
The fossil was brought back to Cambridge so that it could be examined in detail. It was compared with all previous records and revealed new information about the animal’s habitat and evolution. The animal can be seen to have only existed in places that were once located at the Equator, such as Great Britain during the Carboniferous. Previous reconstructions have suggested that the animal lived in coal swamps, but this specimen showed Arthropleura preferred open woodland habitats near the coast.
Although this is the largest Arthropleura fossil skeleton ever found, there is still much to learn about these creatures. “Finding these giant millipede fossils is rare because once they died, their bodies tend to disarticulate, so it’s likely that the fossil is a molted carapace that the animal shed as it grew,” said Davies. “We have not yet found a fossilized head, so it’s difficult to know everything about them.”
The researchers believe that to get to such a large size, Arthropleura must have had a high-nutrient diet. “While we can’t know for sure what they ate, there were plenty of nutritious nuts and seeds available in the leaf litter at the time, and they may even have been predators that fed off other invertebrates and even small vertebrates such as amphibians,” said Davies.
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