2018 started for Professor Neil Davies, from the Department of Earth Sciences at the University of Cambridge, with a surprise of epic dimensions. In the metaphorical sense. And in the most literal of the expression. During a walk with their PhD students along the beaches of Northumberland, in north-west England, near the Scottish border, the group came across a sandstone rock marked by what appeared to be a large fossil. The find, Davies confesses, was “fortuitous” and left the team intrigued. After months of study, their conclusions have just been revealed in an article published in Journal of the Geological Society. What Davies and his students found by chance are the remains – one of the few that remain – of * Arthropleura *, a Carboniferous Period millipede the size of a car.
With the one located on the shores of Northumberland scientists add only three fossils showing the segments of the exoskeleton of the Arthropleura, invertebrates similar to current millipedes except for their exorbitant size. “Finding them is rare because once their bodies die they tend to disarticulate,” explains Davies, who believes, precisely for this reason, that the remains located on the border with Scotland may show a molting of the shell that eventually fell off. “We have not yet found a fossilized head, so it is difficult to know everything about them.” The Cambridge team’s discovery is not important just because of the scarcity of fossils from ArthropleuraIt is also due to its own characteristics.
The oldest and largest fossil
The specimen is older and larger than the other two fossils that scientists had found so far, both in Germany. The segment discovered about 40 miles north of Newcastle measures about 75 centimeters long, which leads experts to think that the original creature could reach a length of 2.7 meters, a width of 55 centimeters and a weight of approximately 50 kilos, measures worthy of a python.
The fossil –collects a statement from the University of Cambridge– reveals to experts that Arthropleura outnumbers even ancient sea scorpions (Eurypterid), making them the largest known invertebrate animal of all time. The creature dates to the Carboniferous Period, some 326 million years ago, long before the Age of Dinosaurs.
Although Northumberland is a cool, humid region today, plagued by freezing winters and mild summers, during the Carboniferous Period, when Great Britain was near the Equator, its climate was more tropical. Invertebrates like Arthopleura and the first amphibians lived on the scattered vegetation around streams and rivers. The 2.7 m specimen discovered by Davies’ team was actually located in a fossilized river channel. The researchers believe that the segment, likely a molt, was filled with sand, which facilitated its preservation.
“It was an incredibly exciting find, but the fossil is so big that to get it up to the cliff it took four of us to get”, recalls the professor of Sedimentary Geology. The piece, located in a sandstone block on Howick Bay Beach, where it fell after detaching from a cliff, was removed in May 2018 with permission from local authorities and it was moved to Cambridge so that investigators could examine it.
During their study, the experts reached relevant conclusions. Scientists believe, for example, that Arthropleura that they only occupied places that were located in Ecuador, as happened with Great Britain during the Carboniferous; and although they valued that it inhabited coal swamps, the new specimen seemed to prefer the open forests near the coast.
One of the questions the researchers are trying to answer is the reason for the enormous size of the Arthropleura. One of the explanations they handle is an increase in oxygen during the late Carboniferous and Permian periods, but since the new fossil was located in rocks deposited before that increase, scientists believe that it cannot be the only cause.
Another hypothesis targets your diet, rich in nutrients. In the Cambridge University statement, Davies explains that there is no certainty about what the Arthopleura, but the abundance of nuts and seeds slips into the litter of the area or even the possibility that they fed on other invertebrates and small vertebrates, like amphibians.
Waiting to shed more light on how giant millipedes were and lived – another question that experts are asking is what motivated its extinction in the Permian-, the huge fossil found by Davies and his team will be on display from 2022 at the Sedgwick Museum in Cambridge.
Images | Neil davies