Systematics of the scimitar babblers (Pomatorhinus: Timaliidae): Phylogeny, biogeography, and species-limits of four species complexes

Monophyly of the scimitar babblers (Pomatorhinus, Xiphirhynchus: Timaliidae), traditionally defined by the characteristic of having long, curved bills, has been questioned by recent molecular phylogenetic results. We examined representatives of all scimitar babbler species complexes, including all distinct lineages of four complexes as well as several potential relatives, and corroborate that Xiphirhynchus and some species of Stachyris group within Pomatorhinus. Pomatorhinus species comprise three separate clades: larger scimitar babblers (Pomatorhinus hypoleucos, Pomatorhinus erythrogenys complexes); orange- and coral-billed scimitar babblers (Pomatorhinus ochraceiceps, Pomatorhinus ferruginosus complexes); and small scimitar babblers (Pomatorhinus schisticeps, Pomatorhinus ruficollis, Pomatorhinus horsfieldii, Pomatorhinus montanus complexes). Additionally, at least two of the traditional species complexes are not monophyletic. Lineages of the ruficollis and schisticeps groups are intertwined, and P. montanus and P. horsfieldi group within the schisticeps complex. Upon revision of four traditional species complexes, P. hypoluecos, P. ferruginosus, P. schisticeps, and P. ruficollis (with 41 subspecies described in total), 27 distinct, independent lineages or phylogenetic species were distinguished. Two contrasting biogeographical patterns are evident in these groups: Sino-Himalayan areas are either sister to south-east Asian areas or are embedded within a clade of other Asian areas. The present study demonstrates the need for unraveling the confusion in traditional taxonomy to allow the study of complex biodiversity patterns in tropical Asia.