The most complete ankylosaur skull ever found in the Wessex Sub-basin (Lower Cretaceous) of the Isle of Wight.

Ankylosaur remains are frequently recovered from the Lower Cretaceous Wealden deposits of the Isle of Wight, although the vast majority of these fossils represent postcranial elements and osteoderms. The rarity of ankylosaur cranial material means any new specimens are important for understanding the morphology, palaeoecology and evolution of these taxa. Here we describe a well-preserved partial ankylosaur cranium recovered with associated ankylosaur remains from the Wessex Formation at Compton Bay. This is the most complete ankylosaur skull ever recovered from the Wessex Sub-basin and is now held at Dinosaur Isle Museum (DI), Sandown, IOW. A highly water worn specimen held at the Sedgwick Museum of Earth Sciences was found at Chilton Chine in the early 1990s and assigned to cf. Polacanthus, and the two crania are compared here.

The specimen consists of the posterior part of the basicranium and skull roof including the proximal paraoccipital processes, occipital condyle and basal tuberosity. Both skulls share characters including the position of some of the foramina exiting the endocranium and lateral curvature of the skull roof. The DI skull differs from the Sedgwick specimen by the presence of a well-defined, notched border of the supraoccipital, flat rostal-caudal dorsal cranial surface, the occipital condyle being more bulbous and angled more ventrally, a well-defined nuchal shelf and being smaller and less robust. Differences between the specimens may be due to sexual dimorphism, ontogeny or they may represent different taxa.