David K. Yeates, CSIRO Entomology PO Box 1700 Canberra AUSTRALIA.
Rudolf Meier, Department of Biological Sciences, National University of Singapore, SINGAPORE.
Brian Wiegmann, Department of Entomology, North Carolina State University, Raleigh NC USA.
The insect order Diptera (true flies) is one of the most species rich, anatomically varied and ecologically innovative groups of organisms, making up around 12% of the known animal species. An estimated 125,000 species of Diptera have been described, however, the total number of extant fly species is many times greater. The living dipteran species have been classified into about 10,000 genera, 150 families, 22-32 superfamilies, 8-10 infraorders and 2 suborders (Yeates & Wiegmann, 1999). The monophyly of Diptera is well established. Hennig (1973) lists 37 autapomorphies some of which form morphologically complex structures such as the specialized mouthparts adapted for sponging liquids. Traditionally, the best-known autapomorphy is the transformation of the hind wings into halteres, but this character may now be in need of reinterpretation due to recent phylogenetic research suggesting a sister group relationship between Strepsiptera and Diptera (Whiting et al. 1997). This work implies homology between the Diptera halteres and Strepsiptera pseudohalteres. The sister group of Diptera remains unknown. Morphology suggests either Mecoptera, Siphonaptera, or a monophylum consisting of both, but based on the aforementioned molecular evidence the Strepsiptera has to be added to the list of candidate taxa. The first fossils attributable to Diptera are known from the Permian, and a large number of fossil Diptera are known from the Mesozoic (Yeates & Wiegmann, 1999).