Open Paleo

Torosaurus

Marsh, 1891 TOR-o-SAWR-us Disputed

From Greek toros, "perforated" or "full of holes", combined with Greek sauros, "lizard" — means "perforated lizard", in reference to the large openings in its frill

72.2–66.0 million years ago Maastrichtian, Late Cretaceous
Late Cretaceous stages

Torosaurus is a genus of herbivorous chasmosaurine ceratopsian dinosaur that lived during the late Maastrichtian age of the Late Cretaceous period, between 68 and 66 million years ago, though it is possible that the species range might extend to as far back as 69 million years ago. Fossils have been discovered across the Western Interior of North America, from as far north as Saskatchewan to as far south as Texas.

Under dispute

Whether Torosaurus is a valid genus or the fully mature growth stage of Triceratops is contested. Scannella and Horner (2010) argued from frill ontogeny and bone histology that all known Torosaurus skulls are senescent Triceratops, formally synonymizing the two. Longrich (2011) and Longrich and Field (2012) rejected the synonymy on the absence of transitional forms, and Maiorino and colleagues (2013) on morphometric grounds. Mallon and colleagues (2022) described a Torosaurus they judged a late subadult or early adult (EM P16.1) and concluded that the evidence weighs in favor of two genera, while noting that younger Torosaurus are needed to reject the synonymy outright. A phylogenetic analysis by Dalman and colleagues (2022) recovered Torosaurus latus outside the clade containing the Triceratops species. No broad consensus has been reached.

Diagnosis

  1. Posterior crest perforated by pair of large supra-temporal fontanelles in parietals
  2. Squamosal bones very long and slender, showing sutures only near distal ends
  3. Main horn-cores placed well back of orbit
  4. Nasal horn-core short with compressed apex directed forward

Species

Torosaurus latus Marsh, 1891 Disputed

Type species

From Latin 'latus' meaning 'wide', in reference to the broad frill of the skull.

Holotype
YPM 1830 , Yale Peabody Museum of Natural History
Material
One skull and parts of skeleton.
Horizon
Lance Formation, Maastrichtian, Late Cretaceous , 72.2–66.0 million years ago
Locality
north side of Lightning Creek, about 2 miles above the mouth of that stream, Wyoming, United States

Notable specimens

  • “Adam”

    EMK-0001 Museum of Evolution, Knuthenborg largest individual

    Well-preserved Torosaurus skull, the largest known at 3 meters long, surpassing the earlier large referred skulls; first put on display in 2023.

    Cantrell & Suazo (2025)

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.

    Places the type on "the north side of Lightning Creek, about 2 miles above the mouth of that stream", in what it calls the Laramie.

    hatcher1907a
  2. Cantrell, A. K.; Suazo, T. L. (2025). Collecting the world's largest known dinosaur skull. New Mexico Geological Society Guidebook 199-208. doi:10.56577/FFC-75.199

    75th Fall Field Conference, Geology of the Eastern San Juan Basin.

    cantrell2025a
  3. Marsh, O. C. (1891). Notice of new vertebrate fossils. American Journal of Science s3-42(249): 265-269. American Journal of Science (AJS). doi:10.2475/ajs.s3-42.249.265 marsh1891a
  4. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Source of the hip height estimate, and the appearance features.

    jones2026a
  5. Dalman, S. G.; Jasinski, S. E.; Lucas, S. G. (2022). A new chasmosaurine ceratopsid from the Upper Cretaceous (Campanian) Farmington Member of the Kirtland Formation, New Mexico. New Mexico Museum of Natural History and Science Bulletin 90: 127-153.

    Phylogenetic analysis recovers Torosaurus latus within Triceratopsini, outside the clade containing the Triceratops species.

    dalman2022a
  6. Scannella, J.; Horner, J. R. (2010). Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny. Journal of Vertebrate Paleontology 30(4): 1157-1168. doi:10.1080/02724634.2010.483632

    Argued Torosaurus skulls are senescent Triceratops, synonymizing the two.

    scannella2010a
  7. Longrich, N. R. (2011). Titanoceratops ouranos, a giant horned dinosaur from the late Campanian of New Mexico. Cretaceous Research 32(3): 264-276. Elsevier BV. doi:10.1016/j.cretres.2010.12.007

    Argued Torosaurus is distinct from Triceratops.

    longrich2011a
  8. Longrich, N. R.; Field, D. J. (2012). Torosaurus is not Triceratops: ontogeny in chasmosaurine ceratopsids as a case study in dinosaur taxonomy. PLoS ONE 7(2): e32623. Public Library of Science (PLoS). doi:10.1371/journal.pone.0032623

    Ordered Torosaurus and Triceratops skulls by maturity, found mature and immature individuals of both and no intermediate frills, and concluded Torosaurus is a distinct genus.

    longrich2012b
  9. Maiorino, L.; Farke, A. A.; Kotsakis, T.; Piras, P. (2013). Is Torosaurus Triceratops? Geometric morphometric evidence of Late Maastrichtian ceratopsid dinosaurs. PLoS ONE 8(11): e81608. Public Library of Science (PLoS). doi:10.1371/journal.pone.0081608

    Rejected the Torosaurus-Triceratops synonymy on morphometric grounds.

    maiorino2013a
  10. Mallon, J. C.; Holmes, R. B.; Bamforth, E. L.; Schumann, D. (2022). The record of Torosaurus (Ornithischia: Ceratopsidae) in Canada and its taxonomic implications. Zoological Journal of the Linnean Society 195(1): 157-171. Oxford University Press (OUP). doi:10.1093/zoolinnean/zlab120 mallon2022a