Extant beaked whales perform deep dives to forage for squids. We studied the morphology of the fossil ziphiid Messapicetus gregarius to evaluate its ability to perform such dives. Our analysis suggests an enlargement of the pterygoid sinus system in deep divers. In M. gregarius, the pterygoid sinus is enlarged, but other lines of evidence indicate that the coastal environment also represented an important part of its home range.