Arthropleura, the giant millipede-like arthropod

Arthropleura was a long, segmented arthropod that lived in the coal forests of Europe and North America from about 315 to 300 million years ago. Its armoured body, made of overlapping plates over a row of many legs, reached about 2.5 metres in length and half a metre in width, making it the largest land invertebrate known. It was first described from fossils in Germany in 1854. Its tracks, called Diplichnites, are found in Scotland, Canada and elsewhere.

For more than a century its relationships were unclear, since few fossils included a head. In 2024 Mickael Lheritier and colleagues used synchrotron X-ray scans on the head of a young Arthropleura from Montceau-les-Mines in France, about 300 million years old, and concluded that it belongs near the millipedes among the myriapods. Fossil droppings with plant spores suggest it ate plants, though some scientists think it ate small animals too. The giant's size was likely supported by high oxygen levels, warm swamps and few predators on land. Arthropleura vanished in the Permian, when the coal forests dried out.