Open Paleo

Stegoceras

Lambe, 1902 ste-GOS-er-as

From Greek 'stege' (στέγη) meaning 'roof' and 'keras' (κέρας) meaning 'horn'; meaning 'horn roof', referring to the domed skull.

83.6–72.2 million years ago Campanian, Late Cretaceous
Late Cretaceous stages

Stegoceras is a genus of pachycephalosaurid (dome-headed) dinosaur that lived in what is now North America during the Late Cretaceous period, about 77.5 to 74 million years ago (mya). The first specimens from Alberta, Canada, were described in 1902, and the type species Stegoceras validum was based on these remains. The generic name means "horn roof", and the specific name means "strong". Several other species have been placed in the genus over the years, but these have since been moved to other genera or deemed junior synonyms. Currently only S. validum and S. novomexicanum, named in 2011 from fossils found in New Mexico, remain. The validity of the latter species has also been debated, and it may not even belong to the genus Stegoceras.

Diagnosis

  1. Dome-shaped upper surface of cranial bones
  2. Transverse suture dividing bones into anterior and posterior halves
  3. Symmetrical, compact paired bones situated in median line ahead of nasals
  4. Anterior end produced forward with two projections on larger specimen
  5. Nodose surface texture on anterior and lateral-posterior regions

Species

Stegoceras validum Lambe, 1902

Type species

From Latin 'validus' meaning 'strong' or 'powerful'.

Lectotype
CMN 515 , Canadian Museum of Nature
Material
Nearly complete frontoparietal.
Notes
Lambe (1902) named the species on three frontoparietals without naming a type. Hatcher and colleagues (1907) list CMN 515 and 1423 as the type, and Sullivan (2003) gives CMN 515 as the lectotype.
Horizon
Dinosaur Park Formation, Campanian, Late Cretaceous , 83.6–72.2 million years ago
Locality
East side of the Red Deer River below the mouth of Berry Creek, Alberta, Canada

Synonyms of the genus

Name Type Reason
Gravitholus junior subjective Dyer and colleagues (2023) re-examined the holotype dome and found it a late-stage growth form of Stegoceras validum, its width and proportions being allometric and its parietal depression pathological; Woodruff and colleagues (2025) agree and exclude it from analysis.
Ornatotholus junior subjective Now generally interpreted as a juvenile Stegoceras.

Notable specimens

  • UALVP 2

    University of Alberta Laboratory for Vertebrate Paleontology Found 1926 by George F. Sternberg most complete

    The most complete known individual of Stegoceras, a complete skull with associated postcranial remains and the basis of most scientific understanding of the genus. Its preservation includes ossified soft tissue in the nasal cavity, and it is the model for dome, feeding, and limb studies.

    Gilmore (1924)Sullivan (2003)

  • AMNH 5450

    American Museum of Natural History ontogeny

    A flattened dome long central to the ontogeny and dimorphism debate. Originally the female morph of Stegoceras, then made holotype of the flat-headed Ornatotholus, it is now interpreted as a juvenile S. validum documenting the flat-to-domed growth transition.

    Goodwin et al. (1998)Schott et al. (2011)

References

  1. Hatcher, J. B.; Marsh, O. C.; Lull, R. S. (1907). The Ceratopsia. Monographs of the United States Geological Survey 49: 1-300. United States Geological Survey.

    Records that Lambe "failed to designate any one of these remains as the type", and lists CMN 515 and 1423 as the type.

    hatcher1907a
  2. Gilmore, C. W. (1924). On Troodon validus, an orthopodous dinosaur from the Belly River Cretaceous of Alberta, Canada. Department of Geology, University of Alberta Bulletin 1: 1-43. gilmore1924c
  3. Sullivan, R. M. (2003). Revision of the dinosaur Stegoceras Lambe (Ornithischia, Pachycephalosauridae). Journal of Vertebrate Paleontology 23(1): 181-207. Informa UK Limited. doi:10.1671/0272-4634(2003)23[181:rotdsl]2.0.co;2 sullivan2003b
  4. Goodwin, M. B.; Buchholtz, E. A.; Johnson, R. E. (1998). Cranial anatomy and diagnosis of Stygimoloch spinifer (Ornithischia: Pachycephalosauria) with comments on cranial display structures in agonistic behavior. Journal of Vertebrate Paleontology 18(2): 363-375. doi:10.1080/02724634.1998.10011064 goodwin1998a
  5. Schott, R. K.; Evans, D. C.; Goodwin, M. B.; Horner, J. R.; Brown, C. M.; Longrich, N. R. (2011). Cranial ontogeny in Stegoceras validum (Dinosauria: Pachycephalosauria): a quantitative model of pachycephalosaur dome growth and variation. PLOS ONE 6(6): e21092. Public Library of Science (PLoS). doi:10.1371/journal.pone.0021092 schott2011a
  6. Lambe, L. M. (1902). New genera and species from the Belly River Series (mid-Cretaceous). Geological Survey of Canada Contributions to Canadian Palaeontology 3(2): 25-81. doi:10.5281/zenodo.3233762 lambe1902a
  7. Dyer, A. D.; Powers, M. J.; Currie, P. J. (2023). Problematic putative pachycephalosaurids: synchrotron microCT imaging shines new light on the anatomy and taxonomic validity of Gravitholus albertae from the Belly River Group (Campanian) of Alberta, Canada. Vertebrate Anatomy Morphology Palaeontology 11: 1-33. University of Alberta Libraries. doi:10.18435/vamp29388

    Synchrotron microCT and morphometric re-examination of the Gravitholus holotype, sinking that genus and Hanssuesia into Stegoceras validum.

    dyer2023a
  8. Woodruff, D. C.; Horner, J. R.; Goodwin, M. B.; Evans, D. C. (2025). The first pachycephalosaurid from the Late Cretaceous Two Medicine Formation: effects of the Western Interior Seaway on North American pachycephalosaurid evolution. Zoological Journal of the Linnean Society 205(2). Oxford University Press (OUP). doi:10.1093/zoolinnean/zlaf087

    Concurs with the synonymy of Gravitholus, and holds Hanssuesia pending a fuller ontogenetic assessment.

    woodruff2025a
  9. Paul, G. S. (2024). The Princeton Field Guide to Dinosaurs (3rd ed.). Princeton University Press.

    Source of the appearance features.

    paul2024a