Prenocephale

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.

Prenocephale Temporal range: Late Cretaceous, 70–66 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Holotype skull ZPAL MgD-I/104
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Clade:	†Ornithischia
Clade:	†Pachycephalosauria
Family:	†Pachycephalosauridae
Subfamily:	†Pachycephalosaurinae
Genus:	†Prenocephale Maryańska & Osmólska, 1974[1]
Species
†P. prenes Maryńska & Osmólska, 1974 (type)
Synonyms
Homalocephale? Maryanska & Osmólska, 1974

Discovery

The holotype specimen, Z. Pal. No. MgD-I/104, consists of an isolated yet well-preserved skull, dorsal vertebrae and ribs, sacrum, femora, and caudal vertebrae. It was discovered by the Polish-Mongolian Paleontological Expedition and was found at the Nemegt locality, in a sandstone layer of the Nemegt Formation.^[1] Additional specimens have been recovered from the Bügiin Tsav, Guriliin Tsav, and Tsaagan Khushuu localities of the formation.^[2]

Description

Size compared to a human

Adult Prenocephale measured 2.2 m (7.2 ft) in length and 40 kg (88 lb) in body mass.^[3] 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.^[4]

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.

Life restoration

Classification

Undescribed putative Prenocephale specimen

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.^[5] However, Longrich et al. (2010) and Schott and Evans (2016) kept Sphaerotholus as a distinct genus based on cladistic analysis.^[6][7]

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.^[2]

Below is a cladogram modified from Evans et al., 2013.^[8]

Pachycephalosauria	Wannanosaurus yansiensis Pachycephalosauridae Colepiocephale lambei Hanssuesia sternbergi Stegoceras novomexicanum Stegoceras validum Goyocephale lattimorei Homalocephale calathocercos Tylocephale gilmorei Foraminacephale brevis Amtocephale gobiensis Acrotholus audeti Prenocephale prenes Alaskacephale gangloffi Pachycephalosaurus wyomingensis Sphaerotholus buchholtzae Sphaerotholus goodwini

Paleoenvironment

Prenocephale lived in what is now the Nemegt Formation, in high upland forests, not the dry deserts of Mongolia nowadays.^[9]

See also

• Dinosaurs portal

• Timeline of pachycephalosaur research