Arthropleura

Arthropleura was a genus of giant, extinct millipede-like arthropods that inhabited the lush, oxygen-rich coal forests of the Carboniferous Period. As the largest known terrestrial invertebrate of all time, it represents a pinnacle of arthropod gigantism. The most famous species, Arthropleura armata, could reach an astonishing length of up to 2.3 meters (7.5 feet) and a width of 50 centimeters (20 inches), making it a truly formidable presence on the forest floor. Its body was composed of approximately 30 flattened, articulated segments, each bearing a pair of legs, protected by a tough, jointed exoskeleton. Despite its intimidating size, Arthropleura was likely a herbivore. Fossilized gut contents and coprolites (fossilized dung) contain spores and fragments of lycopod trees and ferns, suggesting it fed on decaying plant matter and nutrient-rich vegetation. Its ecological role was likely similar to that of modern millipedes: a crucial decomposer, breaking down plant material and recycling nutrients within its ecosystem. The immense size of Arthropleura and other Carboniferous arthropods is attributed to the period's significantly higher atmospheric oxygen levels (around 35% compared to today's 21%), which allowed their relatively inefficient respiratory systems to support larger bodies. Fossils of Arthropleura are primarily trace fossils—impressive trackways left in ancient mud—as its body segments tended to disarticulate after death. The discovery of a large, intact body fossil in Northumberland, UK, in 2018 provided unprecedented insight into its anatomy. Arthropleura is a vital subject of study, offering a window into a unique period of Earth's history when environmental conditions allowed invertebrates to achieve sizes unparalleled before or since.