Fig. 10. 3D in The First Reconstruction of the Head Anatomy of a Cretaceous Insect, †Gerontoformica gracilis (Hymenoptera: Formicidae), and the Early Evolution of

Fig. 10. 3D reconstructions of the mandible of †Gerontoformica gracilis (A and D) and Formica rufa (B, C, and E) illustrating our two hypotheses for the evolution of the shovel-shaped mandible of crown ants.According to hypothesis 1 (A → B), the position of the subapical tooth (purple dot in A) is shifted posteriorly so that the margin between it and the apical tooth (cyan dot) is elongated and additional teeth are inserted. Elongation of the masticatory margin (cyan line) leads to the modified orientation of the basal margin (purple line).The original subapical tooth becomes the basal margin (purple dot in B). According to hypothesis 2 (A → C), basal broadening of the mandibular blade leads to the formation of the basal angle and part of the original basal margin is incorporated with the masticatory margin, developing denticles.The original subapical tooth (purple dot in A) remains the subapical tooth (purple dot in B).The position of the fimbriate line on the inner surface of the mandible (purple outline in D and E) supports hypothesis 2.