Arthropleura
| Class | Diplopoda (or stem-group) |
| Age | ~315–299 Ma (Late Carboniferous–Early Permian) |
| Length | Up to ~2.6 meters |
| Diet | Herbivore / detritivore |
| Fossil Sites | Mazon Creek and others in Europe |
| Note | Not an insect, but an arthropod of the same era |
Arthropleura is not technically an insect — it was a giant millipede-like arthropod (myriapod) — but it is included here because it shared the Carboniferous world with giant insects and illustrates the same phenomenon of oxygen-driven gigantism. At lengths of up to 2.6 meters, Arthropleura is the largest known land arthropod in Earth's history.
Description
Arthropleura had a long, segmented body composed of approximately 30 segments, each bearing a pair of legs. Unlike modern millipedes, which have two pairs of legs per body segment, Arthropleura appears to have had one pair per segment, more similar to centipedes, though its exact classification within the myriapods remains debated. The body was broad and flattened, armored with thick cuticle plates.
Complete body fossils of Arthropleura are rare, but large trackway fossils — trails left by the animal walking across soft sediment — are more common and have been found across Europe and North America. A remarkably large fossil trackway found in northern England in 2021 suggested an individual over 2.5 meters long, confirming the extreme size of this animal.
Diet and Ecology
Despite its enormous size, Arthropleura was likely a peaceful herbivore or detritivore. Fossil gut contents associated with some specimens contain fragments of lycopsid (scale tree) bark and spores, suggesting it fed on the abundant plant material on the Carboniferous forest floor. There is no evidence of predatory behavior.
Arthropleura inhabited the coal swamp forests of tropical Euramerica. Its large size and thick armor would have made it virtually invulnerable to the predators of the time, which were mostly amphibians and other arthropods.
Why So Large?
Like the giant insects of the Carboniferous, Arthropleura's enormous size was enabled by the high oxygen levels of the Late Carboniferous atmosphere. Myriapods, like insects, breathe through a tracheal system, and higher oxygen concentrations allow larger body sizes. The decline in oxygen during the Permian is thought to be a factor in Arthropleura's extinction, which occurred around the Carboniferous-Permian boundary.
Significance
Arthropleura demonstrates that the Carboniferous gigantism phenomenon was not limited to insects. A wide range of terrestrial arthropods grew to enormous sizes during this period, all enabled by the same atmospheric conditions. It serves as a vivid illustration of how environmental factors can dramatically reshape the size and form of animal life.