A passage through India: the biotic ferry model supports the build-up of Indo-Australian biodiversity of an ancient soil arthropod clade

Aim: Scutigeromorpha is a globally distributed, ancient group of centipedes with at least 400 million years of evolutionary history. We assess the biogeographic history of the order, with a particular focus on the Peninsular Indian Plate (PIP), a Gondwanan fragment. We hypothesize that continental vicariance explains the disjunct distribution of extant scutigeromorphs, that PIP scutigeromorphs are of ancient Gondwanan origins, and that East Gondwana vicariance explains the diversification of the subfamily Thereuoneminae into its Asian and Australian clades. Location: Global. Taxa: Centipedes, Scutigeromorpha. Methods: We use a novel molecular dataset sampled across the PIP and a global sequence database representing the geographic distribution of all families and subfamilies. We employ molecular phylogenetic analyses on two mitochondrial and three nuclear markers, molecular species delimitation and ancestral range estimation to reconstruct biogeographic history. Results: Ancestral scutigeromorphs were likely widely distributed across Gondwana and diverged prior to any continental vicariance. Scutigeromorph biogeography is shaped by continental vicariance, long-distance dispersal and jump dispersal, indicating an ability to colonize areas far from their ancestral range. The PIP emerged as the ancestral range of Thereuoneminae, which started diversifying during the Cretaceous Period. Subsequent in-situ diversification within the PIP and dispersals into Asia, Australia, and the Pacific Islands best explained the extant distribution of Thereuoneminae, more so than East Gondwana vicariance. Main conclusions: The in-situ diversification of PIP species and their ancient divergence suggest they represent Gondwanan relicts in a landmass whose biota is primarily dispersal-driven. A single dispersal event from the PIP generated most of the extant diversity in Australia, another Gondwanan fragment. Furthermore, the discovery of 11 putative species from the PIP and the Andaman Islands, five times more than was known, highlights the Wallacean and Linnean shortfalls in tropical Asia.