The fossil was discovered in January 2018 in a piece of sandstone that fell off a cliff on Howick Bay Beach in Northumberland. The rock opened and the fossil was revealed.
“It was a complete accidental find,” said Neil Davies, professor of sedimentary geology in the University of Cambridge’s Department of Earth Sciences, who said the fossil was found by a former PhD student.
“It was an incredibly exciting find, but the fossil is so large that it took four of us to move it to the cliff face,” Davies continued.
The fossilized remains of the creature, called Arthropleura, date back to the Carboniferous period about 326 million years ago. This was more than 100 million years before the appearance of the dinosaurs.
When alive, the creature was estimated to be 55 cm (22 in) wide, 2.63 m (8.6 ft) long, and weigh 50 kg (110 lb). That would make them the largest invertebrates ever known – larger than the ancient sea scorpions that held that title, the statement said. Invertebrates are animals that do not have a backbone.
“This is definitely the biggest mistake that has ever existed,” Davis confirmed via email.
It is only the third fossil that has been discovered from Arthropleura. The other two were found in Germany and were much smaller than the new specimen.
To reach this size, they must have eaten a nutritious diet. At that time, the territory of Britain was on the equator, and early invertebrates and amphibians probably lived on plants that grew in a series of streams and rivers.
Researchers believe that the fossilized skeleton was most likely an altered exoskeleton fragment filled with sand, which preserves it.
“It’s rare to find these giant millipede fossils, because once they’re dead, their bodies tend to disintegrate (separate at the joints), so it’s likely that the fossil was a silent shell that the animal expelled as it was growing,” Davies added. “We haven’t found a fossilized head yet, so it’s hard to know everything about it.”
Arthropods crawled for 45 million years before becoming extinct. It is not known exactly why they disappeared, but it may be due to climate change that does not suit them. Or it can happen during the ascent of reptiles, which have come to dominate the same type of habitat.
The fossil will be on display to the public at the Sedgwick Museum in Cambridge in 2022. The research has been published in the Journal of the Geological Society.
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