Head anatomy and phylogenomics show the Carboniferous giant Arthropleura belonged to a millipede-centipede group

The Carboniferous myriapod Arthropleura is the largest arthropod of all time but its fossils are usually incomplete, limiting the understanding of its anatomy, ecology and relationships. MicroCT applied to exceptionally preserved specimens from the Carboniferous Montceau-les26 Mines Lagerstätte (France) reveals unprecedented details of its functional anatomy such as the head and mouthparts. Arthropleura shares features both with millipedes and centipedes. New total-evidence phylogeny combining morphological and transcriptomic data resolves Arthropleura alone as a stem-group millipede, but the inclusion of the highly incomplete Siluro-Devonian Eoarthropleura draws it deeper into the myriapod stem. Arthropleura suggests transitional morphology between clades united primarily by molecular information, and underscores the value of total evidence phylogenetics to understanding evolutionary history.