On the systematic position of a highly derived Amphiesmenoptera insect from Burmese amber (Insecta: Amphiesmenoptera)

Amphiesmenoptera combine the orders Trichoptera and Lepidoptera. Dating analyses based on molecular chronograms across many Lepidoptera groups yielded different results for the early divergence in Lepidoptera spanning a period from 215 Ma (late Triassic) to 160 Ma (late Jurassic). Also, the origin or time of the basal split of both orders cannot be determined with a better precision from the fossil record. The descriptions of Mesozoic fossils are almost always based on wing venation, a character insufficient to discriminate between Trichoptera and Lepidoptera. The oldest Lepidoptera species are supposed to be Archaeolepis mane Whalley, 1985 from the Lower Lias of Dorset (England) and two species from the Upper Lias of Grimmen (NE Germany), which were tentatively assigned to Micropterigidae. The assignment of these Early Jurassic species to Lepidoptera is based solely on the observation of wing scales. In the absence of any other distinguishing characters the presence of scales is regarded as the principal trait that defines Lepidoptera and separates the group from remaining Amphiesmenoptera, including Trichoptera. We follow this view here, and consider a small amphiesmenopteran insect from Burmese amber with wing scales as a fossil representative of Lepidoptera. With an age of ~100 Ma the Burmese amber is of Early Cretaceous origin (Albian). At that time, the evolution of the Lepidoptera had been under way for 55 Ma and the extant family Micropterigidae already existed. The Micropterigidae, together with extant Agathiphagidae and Heterobathmiidae are the basalmost groups of Lepidoptera (= Aglossata). Their systematic position is based on a number of apomorphies and groundplan characters. In contrast to the rest of the Lepidoptera, the adult moths retained functional mandibles and an undifferentiated maxilla.The specimen from Burmese amber is relatively well preserved and allows the examination of important character complexes. The insect is described in detail, and photos and line drawings are provided for wing venation, head, mouthparts, legs and abdomen. All characters shared with primitive Lepidoptera are symplesiomorphies or groundplan traits of Amphiesmenoptera. In contrast, the Burmese fossil has a number of remarkable autapomorphies giving it an appearance that deviates strongly from Lepidoptera and Trichoptera. The species, representing a family of its own, is provisionally placed at the base of the Lepidoptera phylogeny together with the Aglossata. An alternative placement, outside the Lepidoptera, would imply an independent and multiple evolution of wing scales in stem-group Amphiesmenoptera.