Prenocephale (meaning "sloping head"[1]) is a genus of small pachycephalosaurid dinosaur from the Late Cretaceous Nemegt Formation of Mongolia. It was similar in many ways to its close relative, Homalocephale.
Adult Prenocephale measured 2.2 m (7.2 ft) in length and 40 kg (88 lb) in body mass.[2] Unlike the flattened wedge-shaped skull of Homalocephale (a possible juvenile trait also potentially seen in early growth stages of Pachycephalosaurus), the head of Prenocephale was rounded and sloping. The dome had a row of small bony spikes and bumps.[3]
Like some other pachycephalosaurs, Prenocephale is known only from skulls and a few other small bones. For this reason, reconstructions usually depict Prenocephale as sharing the basic body plan common to all of the other Pachycephalosauria: a stout body with a short, thick neck, short forelimbs and tall hind legs.
The head of Prenocephale was comparable to that of Stegoceras, albeit with closed supratemporal fenestrae. Also, the paired grooves above the supraorbitals/prefrontals (along with a posterior parietal that restricts the frontal dome) are absent in Prenocephale. This differentiates the species from Stegoceras, as such features are common in the latter.
Prenocephale is a member of the Pachycephalosauria, a large clade of herbivorous/omnivorous dinosaurs from the Late Cretaceous. Robert Sullivan considered Foraminacephale, "Prenocephale" edmontonensis, and Sphaerotholus goodwini to form a clade with the Asian taxon P. prenes. He considered Tylocephale the sister taxon to the Prenocephale clade, while sinking Sphaerotholus buchholtzae as a subjective junior synonym of "P." edmontonensis. They all possess a distinct row of nodes on the squamosal and parietal areas of the skull roof.[4] However, Longrich et al. (2010) and Schott and Evans (2016) kept Sphaerotholus as a distinct genus based on cladistic analysis.[5][6]
Homalocephale has been viewed as a possible juvenile of Prenocephale due to the lack of a dome and its discovery in the same location and chronological interval, but new specimens of Prenocephale, including a juvenile specimen, suggest that Homalocephale, even if its holotype is a juvenile, is distinct.[7]