A first phylogenetic analysis of Giant Pill-Millipedes (Diplopoda: Sphaerotheriida), a new model Gondwanan taxon, with special emphasis on island gigantism.

The phylogeny of the Giant Pill-Millipedes, order Sphaerotheriida, is investigated using a new morphological character matrix comprising 89 characters. The majority of these characters are employed for the first time in millipedes. All trees obtained agree on the monophyletic status of the Sphaerotheriida and several of its tribes, each restricted to a modern land mass. The species from Madagascar displaying island gigantism do not form a monophyletic group. The classic division of Giant Pill-Millipedes into two families, Sphaerotheriidae and Zephronidae, was not reflected in the analysis. The genus Procyliosoma is the sister-group to all other Sphaerotheriida, rendering the family Sphaerotheriidae paraphyletic. A new family-level classification of Giant Pill-Millipedes, based on the current phylogeny, is introduced. The new family Procyliosomatidae contains only the genus Procyliosoma, distributed in Australia and New Zealand. The family Zephronidae remains unchanged, while the family Sphaerotheriidae now incorporates only the African Giant Pill-Millipede genera. All genera from southern India and Madagascar form a monophyletic group and are placed in the new family Arthrosphaeridae. The Malagasy genus Sphaeromimus is more closely related to the Indian Arthrosphaera species than to other genera from Madagascar. A biogeographical analysis identifies the group as a Gondwana taxon (with a notable absence from South America). The current phylogeny of Giant Pill-Millipede families mirrors perfectly the suggested break-up of Gondwana fragments 160-90 Ma. No evidence for a dispersal event could be found, highlighting the importance of Giant Pill-Millipedes as a potential model taxon.