Figure 6 — CT scans of skulls rendered transparent with pterygoid sinuses highlighted in dark blue. Note that the extension of the preorbital lobe in Semirostrum ceruttii (bottom images) is similar in shape and length to that of the Harbour porpoise (top images). They both differ greatly in width from the Dall’s porpoise, but all three species have longer extensions than those of other extant porpoises. Image modified from Racicot and Rowe (2014, Journal of Paleontology), from specimen CAS 15278 (California Academy of Sciences).