Arthropleura: Giant Carboniferous Arthropod

Arthropleura was a massive relative of modern millipedes that lived in the oxygen-rich forests of the Carboniferous Period. It was two to three meters long and must have weighed hundreds of times as much as modern insects, making it the largest known terrestrial arthropod of all time. Fossils of arthropleura have been uncovered in Nova Scotia, Illinois, Ohio, Pennsylvania, and Scotland. Tracks of these giant arthropods have been found in Nova Scotia and reveal the caterpillar-like movement of arthropleura.

Arthropleura, like the other giant arthropods that lived during the Carboniferous Period, was able to reach its large size because of the way it breathed. Arthropods generally use primitive diffusion organs in their skin called spiracles to diffuse oxygen from the surrounding atmosphere to their bloodstream. These spiracles place a limit on the size an insect or arachnid can reach based on the amount of available oxygen in the atmosphere. Thus, the more oxygen is available, the bigger an arthropod can theoretically become. However, an interesting characteristic of arthropleura is that there have been no imprints of spiracles yet discovered with its fossilized remains. Thus, it is possible that the arthropod could have breathed through lungs (unlikely) or specialized gills adapted for land use (more likely). The lack of terrestrial predators large and strong enough to break through its armor during the Carboniferous may have also contributed to their large size.

These giants resemble modern millipedes in a number of ways. First, they had a body with many segments, just like millipedes. Also, they possessed perhaps as many as thirty pairs of large, spiny legs to carry them across the Carboniferous forest floor. However, they are a bit different from modern millipedes or centipedes. Aside from the obvious difference of size, arthropleura had a very flat body, giving it the appearance of a kind of insect-like surfboard, whereas modern millipedes have a rounder body. They were probably detrivores, feeding on tiny organisms in the decaying matter on the moist, warm forest floor.

The era of the giant arthropods was restricted to the Carboniferous. Toward the end of that Period, the climate was drying out and the great forests were beginning to shrink. As the forests shrank, so did the levels of oxygen in the atmosphere. Unable to retain its size or lifestyle in these moist rainforests, arthropleura died out by the time the Permian Period was ushered in. Never again would arthropods get that big on planet Earth.