Open Paleo

Hanssuesia

Sullivan, 2003 han-SU-see-uh Disputed

Named in honor of paleontologist Hans-Dieter Sues

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

Hanssuesia is a genus of pachycephalosaurid dinosaurs from the late Cretaceous period. It lived in what is now Alberta and Montana, and contains the single species Hanssuesia sternbergi.

Under dispute

Whether Hanssuesia is a junior synonym of Stegoceras validum is unsettled. Dyer and colleagues (2023) found no taxonomically significant morphometric distinction between Hanssuesia sternbergi and Stegoceras validum and proposed synonymy. Woodruff and colleagues (2025) agreed it is probably synonymous, but kept it as a separate terminal in their analysis pending a more detailed ontogenetic assessment.

Diagnosis

  1. Reduced sutural surfaces for squamosal attachment along posterior edges of frontoparietal dome
  2. Incipient parietosquamosal shelf, reduced compared to Stegoceras validum
  3. Frontals proportionally low and broad where in contact with nasals
  4. Lateral frontal lobes not well developed and recessed posterior to medial nasal lobe
  5. Characteristic posterior sloping of parietal portion of frontoparietal dome

Species

Hanssuesia sternbergi (Brown & Schlaikjer, 1943) Disputed

Type species

First named as Troodon sternbergi

Named for Charles Mortram Sternberg, the Canadian paleontologist who found the holotype dome near Steveville, Alberta, in 1928.

Holotype
NMC 8817 , Canadian Museum of Nature
Material
Nearly complete frontoparietal dome with peripheral skull elements
Horizon
Dinosaur Park Formation, Campanian, Late Cretaceous , 83.6–72.2 million years ago
Locality
southeast of Steveville, Alberta, Canada Brown and Schlaikjer (1943) name only the undivided Belly River formation; Sullivan (2003) gives the Dinosaur Park, allowing a remote possibility of the Oldman.

Synonyms

  • Stegoceras sternbergi reassigned

    Interim combination after the species was moved out of Troodon and before Sullivan (2003) erected Hanssuesia.

  • Troodon sternbergi reassigned

    Original combination (Brown and Schlaikjer, 1943) on NMC 8817; later moved to Stegoceras and then to the new genus Hanssuesia by Sullivan (2003).

References

  1. 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

    Revises Stegoceras and erects the genus, as "Hanssuessia"; gives the horizon as the Dinosaur Park Formation, with "a remote possibility that the holotype is from the Oldman Formation".

    sullivan2003b
  2. Brown, B.; Schlaikjer, E. M. (1943). A study of the troödont dinosaurs with the description of a new genus and four new species. Bulletin of the American Museum of Natural History 82(5): 115-150.

    Original description as Troodon sternbergi on NMC 8817; later reassigned to Stegoceras and then to Hanssuesia by Sullivan (2003).

    brown1943a
  3. Sullivan, R. M. (2003). Hanssuesia, the correct generic name for 'Hanssuessia' Sullivan, 2003. Journal of Vertebrate Paleontology 23(3): 714-714. Informa UK Limited. doi:10.1671/03010 sullivan2003a
  4. 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

    Agrees with Dyer and colleagues (2023) that it is probably a synonym of Stegoceras validum, but scores it as a separate terminal pending an ontogenetic study; recovers it as sister to Colepiocephale.

    woodruff2025a
  5. 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

    Found Hanssuesia sternbergi falls within the variation of Stegoceras validum and proposed synonymy.

    dyer2023a