Congruence and controversy: Toward a higher-level phylogeny of diptera

The order Diptera (true flies) is one of the most species-rich and ecologic ally diverse clades of insects. The order probably arose in the Permian, an d the main lineages of flies were present in the Triassic. A novel recent p roposal suggests that Strepsiptera are the sister-order to Diptera. Within Diptera, evidence is convincing for the monophyly of Culicomorpha, Blephari ceromorpha, and Tipulomorpha but weak for the monophyly of the other basal infraorders and for the relationships among them. The lower Diptera (Nemato cera) is paraphyletic with respect to Brachycera, and morphological evidenc e suggests the sister-group of Brachycera lies in the Psychodomorpha. Recen t analyses suggest Tipulomorpha are closer to the base of Brachycera than t o the base of Diptera. Brachycera are undoubtedly monophyletic, but relatio nships between the basal lineages of this group are poorly understood. The monophyly of Stratiomyomorpha, Xylophagomorpha, Tabanomorpha, and Muscomorp ha is well supported. Eremoneura, and its constituent clades Empidoidea and Cyclorrhapha, are monophyletic. The sister-group of Eremoneura is likely t o be part or all of Asiloidea. Several viewpoints on the homology of the ma le genitalia of eremoneuran flies are discussed. Phylogenetic analyses sugg est that lower Cyclorrhapha (Aschiza) are paraphyletic; however, schizophor an monophyly is well supported. The monophyly of Acalyptratae is not well-f ounded and the relationships between acalyptrate superfamilies remain obscu re. Recent advances document the monophyly of the families of Calyptratae a nd the relationships among them. Areas critical to future advances in under standing dipteran phylogeny include the relationships among the basal infra orders of Diptera and Brachycera and the relationships between the superfam ilies of acalyptrates. Progress in dipteran phylogenetics will accelerate w ith the exploration of novel data sources and the formulation of hypotheses in an explicitly quantitative framework.