Open Paleo

Pachycephalosauria

Maryańska & Osmólska, 1974 Type genus Pachycephalosaurus

Its genera lived 121.4–66.0 million years ago Early Cretaceous–Late Cretaceous
Early Cretaceous and Late Cretaceous stages

Pachycephalosauria, meaning "thick-headed lizards," is a clade of ornithischian dinosaurs that together with the horned ceratopsians makes up the group Marginocephalia. Its members were bipedal herbivores and omnivores, mostly small animals in the range of 2 to 3 meters long, and lived exclusively in the Northern Hemisphere during the Cretaceous, with all known genera coming from North America and Asia. They are best known for their heavily ossified skulls, which may be domed, flat, or wedge-shaped depending on the species and are often ringed with bony nodes and spikes. Because most specimens consist only of these durable skull caps, the group is classified almost entirely on cranial features, and flat-headed forms may in some cases represent juveniles of dome-headed adults. The function of the thickened dome has been much debated, with intraspecific head-butting or flank-butting the leading hypotheses. Well-known members include Pachycephalosaurus and Stegoceras.

Diagnosis

  1. Dramatically thickened frontoparietal dome on the skull roof
  2. Peripheral ornamentation of nodes and horns around the dome margin
  3. Wide, shelf-like squamosal
  4. Relatively large orbits
  5. Bipedal stance with stiffened tail
  6. Broad body with flared iliac blades

Clades within Pachycephalosauria

Genera placed directly in Pachycephalosauria

  • Wannanosaurus Hou, 1977 Campanian (83.6–72.2 Ma)Chinaincertae sedis
  • Zavacephale Chinzorig et al., 2025 Aptian–Albian (121.4–100.5 Ma)Mongolia

References

  1. Maryańska, T.; Osmólska, H. (1974). Pachycephalosauria, a new suborder of ornithischian dinosaurs. Palaeontologia Polonica 30: 45-102. Polish Academy of Sciences.

    Erected the clade Pachycephalosauria.

    maryańska1974a
  2. Schott, R. K.; Evans, D. C. (2016). Cranial variation and systematics of Foraminacephale brevis gen. nov. and the diversity of pachycephalosaurid dinosaurs (Ornithischia: Cerapoda) in the Belly River Group of Alberta, Canada. Zoological Journal of the Linnean Society. Oxford University Press (OUP). doi:10.1111/zoj.12465

    Comprehensive systematic analysis of pachycephalosaurid diversity.

    schott2016a