Fig. 2.

Midsaggital cuts of three-dimensional reconstructed heads of the different species in Geospiza obtained by Computed Tomography (CT) scans. (A) Example of a three-dimensional reconstruction of a bird skull obtained by CT showing the plane corresponding to a midsaggital cut. (B) Midsagittal cuts obtained from three-dimensional reconstructions of CT scans for the different species in the genus Geospiza. Color dots label the species. Red arrows show the top-most position of the keratin layer indicating that soft tissue is found beyond this point. (C) Zoom of the upper part of the beak of the Medium Ground Finch (Geospiza fortis) showing the digitized outline of the bone structure of the upper part of the beak (orange curve). (D) Outlines of the bone structure of the upper part of the beak for the different species shown in B collapsed via a nonuniform scaling transformation. The dashed line indicates the position of the divergence point (see main text).