Detailed description of the skull morphology of Winterswijk pachypleurosaurs expands the diagnosis of Anarosaurus heterodontus greatly. A. heterodontus is characterized by a broad and roughly shield-shaped sculptured nasal. The maxilla is separated from the anterolateral frontal processes by the nasal and the largely protruded prefrontal. The parietal in A. heterodontus exhibits a very characteristic lateral process that forms most of the dorsal margin of the upper temporal opening. The squamosal and quadrate are distinctly large and massive. The posterior part of the lower jaw is unusually stout. The pterygoid has an ascending posterior process that is ventrally articulated with the quadrate, supporting the mandibular condyle. The comparison of skull morphology with known pachypleurosaurs shows that A. heterodontus is most similar to Anarosaurus pumilio and Dactylosaurus. On the basis of the massive construction of the posterior part of the skull and the lower jaw, it is hypothesized that Anarosaurus heterodontus was able to crush hard-shelled prey.