Some aspects of mandibular morphology are known for three hesperornithiform genera: Hesperornis, Parahesperornis and Baptornis. All share a distinctive intramandibular joint between the angular and the splenial. A special process of the surangular extending between the splenial and the dentary bridges the joint. The symphysis appears to have been elongate and unfused, joining anteriorly with a short intersymphyseal bone. It appears that the mandibles spread posteriorly as the jaws opened, allowing the swallowing of larger prey. The closed mandible is very slender anteriorly, resembling some cetaceans, and seems highly adapted for the capture of fish. The discovery of fish remains in a preserved stomach cast of Baptornis gives direct support for this interpretation.