If you just look at today's millipede animals, you'll get goosebumps, be thankful that we don't live in the Carboniferous period, about 100 million years before the dinosaurs arrived. Because, at that time millipedes were the size of a car.
Scientists have made an astonishing discovery along England's northeast coast of 326 million-year-old fossils. This fossil shows the largest millipede footprint ever found. It is estimated to be about 2.7 meters long, roughly the same length as the car.
The remains of these millipedes belong to the now-extinct genus Arthropleura of millipede arthropods, and elevate this class of creatures to the largest known invertebrates of all time. The discovery, which was originally announced in 2018, is an opportunity.
"It was a fortuitous find. The way the rock fell, then cracked open and perfectly exposed the fossil. This fossil was coincidentally found by one of our former PhD students while walking through it," said Earth scientist Neil Davies of the University of Cambridge in the UK, quoted by Reuters. from Science Alert, Thursday (23/12/2021).
"It was a very interesting find, but the fossil was so big that the four of us had to carry it up a cliff."
The fossil portion found was 50-75 cm wide, and the team estimated it could weigh around 50 kg. In addition to being a record breaker, the fossil teaches experts more about ancient millipedes.
In the Carboniferous Period, Britain would have been close to the equator, consistent with earlier Arthropleura findings. Only two previous Arthropleura fossils of this type have been found in Germany and are smaller.
These earlier findings also suggest that invertebrates tend to live around coal bogs, large areas with large amounts of biomass that accumulate like peat when they die, eventually turning into coal.
It is generally accepted that today's arthropods (a group that includes insects and millipedes) physically cannot become this large, because oxygen levels are not high enough to facilitate their method of breathing at larger sizes.
However, these fossils are from before the peak of atmospheric oxygen in the late Carboniferous and Permian periods, when the concentration of oxygen in the atmosphere was only 23%, not much higher than the current 21%. This suggests increased oxygen was not the only factor that allowed the arthropods to reach such extraordinary sizes. The researchers then linked Arthropleura's size to a high-nutrient diet and lack of predators.
"Although we don't know for sure what they ate, there were plenty of nutritious nuts and seeds available in the leaves at the time, and they might even have been predators that ate other invertebrates and even small vertebrates like amphibians," Davies said.
Arthropleura animals lived around the equator for approximately 45 million years, becoming extinct during the Permian (299-252 million years ago). The reason for the extinction is unclear, perhaps in part due to the increase in reptiles that eventually overcame them.
The fossil was found in sandstone that fell from a cliff, and was originally in a river channel. This represents a theory that suggests the fossil might be part of the exoskeleton of Arthropleura molting, which was eventually filled with sand that preserved it.
"Finding fossils of these giant millipedes is rare, because once they die, their bodies tend to be disorganized, so it's very likely that the fossil was a molting carapace that the animal shed as it grew," Davies said.
"We haven't found any head fossils, so it's hard to know everything about them," he concluded.