The world’s largest fossil of a massive millipede — the size of a car – has been discovered on a beach in northern England.
Known as Arthropleura, the fossil dates back 326 million years to the Carboniferous Period, more than 100 million years before the Age of Dinosaurs. The fossil reveals that Arthropleura was the largest-known invertebrate animal of all time, larger than the previous record holders, ancient sea scorpions.
The specimen, which was discovered on a Northumberland beach about 40 miles north of Newcastle, is made up of multiple articulated exoskeleton segments that are generally similar in shape to modern millipede exoskeleton segments. It is only the third such fossil to be discovered.
It is also the oldest and longest segment: the segment is roughly 75 centimeters long, but the original monster was estimated to be around 2.7 meters in length and weighed around 50 kilograms.
The findings were published in the Journal of the Geological Society.
The fossil was discovered in a big block of sandstone that had fallen from a cliff to the beach in Howick Bay in Northumberland in January 2018.
“It was a complete fluke of a discovery,” says Dr Neil Davies, 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 PhD students happened to spot when walking by.”
Unlike today’s chilly and wet weather, Northumberland had a more tropical climate during the Carboniferous Period, when Britain was near the Equator. Invertebrates and early amphibians subsisted on the strewn plants that surrounded a network of creeks and rivers. The researchers discovered the specimen in a fossilized river channel: it was most likely a moulted section of the Arthropleura’s exoskeleton that filled with sand and preserved it for hundreds of millions of years.
With permission from Natural England and the Howick Estate, the fossil was excavated in May 2018.
“It was an incredibly exciting find, but the fossil is so large it took four of us to carry it up the cliff face,” adds Davies.
The fossil was returned to Cambridge so that it could be thoroughly investigated. It was compared to all existing data, revealing new details about the animal’s environment and evolution. The animal can be found only in regions that were once near the Equator, such as Great Britain during the Carboniferous period. Previously, it was thought that the animal lived in coal swamps, but this specimen revealed that Arthropleura favored open forest areas near the coast.
Only two other Arthropleura fossils are known, both from Germany and significantly smaller than the new specimen. Despite the fact that this is the largest Arthropleura fossil skeleton yet discovered, there is still much to learn about these critters.
“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 moulted carapace that the animal shed as it grew,” Davies says.
“We have not yet found a fossilised head, so it’s difficult to know everything about them.”
For a long time, it was assumed that the large size of Arthropleura was due to a surge in atmospheric oxygen in the late Carboniferous and Permian periods, but the new fossil reveals that oxygen is not the only explanation.
In order to grow so big, Arthropleura must have had a lot of nutrients in its food.
“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,” Davies adds.
Arthropleura animals crawled around the equatorial part of Earth for about 45 million years before becoming extinct during the Permian epoch. The cause of its extinction is unknown, but it could have been owing to global warming, which caused the temperature to become too dry for them to live, or to the rise of reptiles, which outcompeted them for food and soon controlled the same habitats.
In the coming year, the fossil will be on display in Cambridge’s Sedgwick Museum.
Image Credit: University of Cambridge
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