Three holometabolan adult thorax states. A) A thorax with approximately equally sized pterothoracic segments is possibly ancestral for Aparaglossata (Figure shows thorax of Nannochorista neotropica (Mecoptera, Nannochoristidae); prothorax not shown.). B) shows a thorax of taxa with anteromotorism, i.e., flight with mainly the fore wings (e.g., Hymenoptera, Trichoptera, “higher” Lepidoptera, and Diptera; figure shows Ptychoptera sp. (Diptera, Ptychopteridae)). This state is possibly ancestral for Holometabola. However, the reconstruction of the ancestral state of this character in the formal analysis remained ambiguous for Holometabola and Aparaglossata. C) shows a thorax of taxa with posteromotorism, i.e., flight with the hind wings (Coleoptera and Strepsiptera; figure shows Mengenilla moldrzyki (Strepsiptera, Mengenillidae)). red: muscles. blue: sceleton. green: gut. yellow: nerves. Numerals refer to thoracic segments. th: thorax segment. g: ganglion. dlm: dorsal longitudinal muscle. dvm: dorso-ventral muscle. vlm: ventral longitudinal muscle (not visible in A and B). A 3D version of this figure can be found as Additional file 5 (Click on image to activate animation).