Millipedes are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known
Pneumodesmus newmani, earliest known land animal
scientifically as the class Diplopoda, the name being derived from this feature.
Millipedes are among the first animals to have colonised land during the Silurian period. Early forms probably ate mosses and primitive vascular plants. There are two major groups of millipedes whose members are all extinct: the Archipolypoda ("ancient, many-legged ones") which contain the oldest known terrestrial animals, and Arthropleuridea, which contain the largest known land invertebrates. The earliest known land creature, Pneumodesmus newmani, was a 1 cm (0.4 in) long archipolypodan that lived 428 million years ago in the upper Silurian, and has clear evidence of spiracles (breathing holes) attesting to its air-breathing habits. During the Upper Carboniferous (340 to 280 million years ago), Arthropleura became the largest known land-dwelling invertebrate on record, reaching lengths of at least 2 m (6 ft 7 in).