Arthropleura, an enormous myriapod that lived some 326 million years ago (Carboniferous period), is estimated to have been 55 cm (1.8 feet) in width and up to 2.63 m (8.6 feet) in length, weighing 50 kg.
The giant fossil of Arthropleura — just the third such fossil ever found — 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, England.
The specimen is made up of multiple articulated exoskeleton segments, broadly similar in form to modern millipedes.
It reveals that Arthropleura was the largest-known invertebrate animal of all time, larger than the ancient sea scorpions that were the previous record holders.
There are only two other known Arthropleura fossils, both from Germany, and both much smaller than the new specimen.
“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 Dr. Neil Davies, a researcher in the Department of Earth Sciences at the University of Cambridge.
“We have not yet found a fossilized head, so it’s difficult to know everything about them.”
Previous reconstructions have suggested that Arthropleura millipedes lived in coal swamps, but the new specimen showed they preferred open woodland habitats near the coast.
Dr. Davies and colleagues believe that to get to such a large size, the ancient creature 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,” Dr. Davies said.
“Arthropleura animals crawled around Earth’s equatorial region for around 45 million years, before going extinct during the Permian period.”
“The cause of their extinction is uncertain, but could be due to global warming that made the climate too dry for them to survive, or to the rise of reptiles, who out-competed them for food and soon dominated the same habitats.”
The team’s paper was published today in the Journal of the Geological Society.
Neil S. Davies et al. The largest arthropod in Earth history: insights from newly discovered Arthropleura remains (Serpukhovian Stainmore Formation, Northumberland, England). Journal of the Geological Society, published online December 21, 2021; doi: 10.1144/jgs2021-115
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