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Ceratosaurus

Marsh, 1884 SERR-ah-toe-SOR-uhs /ˌsɛrətoʊˈsɔːrəs/

From Greek 'keras/keratos' (horn) and 'sauros' (lizard); meaning 'horn lizard', referring to the distinctive median nasal horn core.

154.8–143.1 million years ago Kimmeridgian–Tithonian, Late Jurassic
Late Jurassic stages

Ceratosaurus is the type genus of Ceratosauridae and one of the most iconic Late Jurassic theropods of the Morrison Formation. The type species, Ceratosaurus nasicornis, was erected by Othniel Charles Marsh in 1884 on a near-complete skeleton (USNM 4735) collected by M. P. Felch from Quarry No. 1, Garden Park, near Cañon City, Fremont County, Colorado. Originally housed at the Yale Peabody Museum, the holotype was transferred to the USNM in 1898-1899 and prepared by C. W. Gilmore over 1911-1918. Gilmore (1920) produced the canonical redescription as USNM Bulletin 110, correcting Marsh's restoration errors and supporting Ceratosauridae as distinct from Megalosauridae against Cope's 1892 referral. Madsen and Welles (2000) revised the osteology and named two additional Morrison species (C. dentisulcatus from Cleveland-Lloyd, C. magnicornis from the Fruita Paleontological Area), each based on more complete material from upper or lower Brushy Basin Member horizons. Ceratosaurus is most readily diagnosed by an unpaired nasal horn core, smaller paired protuberances above each orbit, an unusually low premaxillary tooth count, a tightly coossified pelvis, coossified metatarsals II-IV, and a row of small dermal ossicles running along the dorsal midline.

Diagnosis

  1. Unpaired median horn core formed from the nasals, transversely compressed and positioned above the external nares.
  2. Paired horn-like protuberances on the lacrimal/prefrontal bones above the antorbital fenestra, partially overhanging each orbit.
  3. Cervical vertebral centra plano-concave (flat anteriorly, deeply cupped posteriorly), with strongly shortened posterior cervicals.
  4. Zygosphene-zygapophysis accessory articulation present in cervical and dorsal vertebrae.
  5. Premaxilla bears only three teeth, an unusually low count among contemporaneous Jurassic theropods.
  6. Pelvis tightly coossified — ilium, pubis, and ischium fused — with a closed obturator foramen on a slender pubis.
  7. Metatarsals II-IV coossified to one another.
  8. Row of small osseous dermal ossicles preserved along the dorsal midline from the base of the skull through the proximal tail.

Species

Ceratosaurus nasicornis Marsh, 1884

Type species

From Latin 'nasus' (nose) and 'cornu' (horn); meaning 'nose-horned', referring to the median nasal horn core.

Holotype
USNM 4735 , National Museum of Natural History, Smithsonian Institution
Material
Near-complete skeleton including the skull and lower jaws, atlas-axis complex, seven cervical and 12 (mostly fragmentary) dorsal vertebrae, sacrum, ~50 caudal vertebrae with chevrons, the coossified pelvis, both femora, the right tibia, fibula, and pes, plus dorsal-midline dermal ossicles.
Horizon
Brushy Basin Member, Morrison Formation, Kimmeridgian–Tithonian, Late Jurassic , 154.8–143.1 million years ago
Locality
Felch Quarry No. 1, Colorado, United States Chure (2000) places Felch Quarry 1 in the Brushy Basin Member, "47.9 m above the J5 unconformity", for two other types from the quarry.

Synonyms

  • Megalosaurus nasicornis reassigned

    Cope (1892) referred Ceratosaurus nasicornis to Megalosaurus; Gilmore (1920) rejected the referral and reaffirmed Ceratosaurus as a valid genus distinct from Megalosaurus.

Notable specimens

  • UMNH VP 5278

    Utah Museum of Natural History Found 1960 by James Madsen complementary

    Fragmentary, disarticulated skeleton with skull from the Cleveland-Lloyd Quarry, Utah, one of the largest known Ceratosaurus individuals, estimated up to about 7 meters long and as much as 1,132 kilograms. Originally the basis of the now-synonymized species C. dentisulcatus.

    Paul (2016)Glut (1997)

  • MWC 1

    Museums of Western Colorado, Dinosaur Journey Found 1976 by Thor Erikson complementary

    Articulated, fairly complete subadult specimen with skull from near Fruita, Colorado, lacking lower jaws, forearms, and gastralia. Includes a well-preserved, CT-scanned braincase. Basis of the now-synonymized species C. magnicornis; one study estimated it as the largest known individual.

    Foster (2020)Sombathy et al. (2025)

  • ML 352, SHN (JJS)-65

    Sociedade de Historia Natural range extension

    Partial skeleton from the Porto Novo Member of the Lourinha Formation at Valmitao beach, Portugal, including femur, tibia, fibula, and teeth. First evidence of Ceratosaurus outside North America. Species assignment is unresolved, ranging from C. dentisulcatus to Ceratosaurus aff. C. nasicornis.

    Mateus & Antunes (2000)

References

  1. Chure, D. J. (2000). A new species of Allosaurus from the Morrison Formation of Dinosaur National Monument (UT-CO) and a revision of the theropod family Allosauridae. Doctoral thesis, Columbia University.

    Gives the Felch Quarry 1 horizon as "Brushy Basin Mbr., 47.9 m above the J5 unconformity".

    chure2000a
  2. Marsh, O. C. (1884). Principal characters of American Jurassic dinosaurs; Part VIII, The order Theropoda. American Journal of Science 27(160): 329-340. American Journal of Science. doi:10.2475/ajs.s3-27.160.329

    Erects Ceratosaurus nasicornis and the family Ceratosauridae on a near-complete skeleton (now USNM 4735) from the Morrison Formation of Garden Park, Colorado.

    marsh1884a
  3. Gilmore, C. W. (1920). Osteology of the carnivorous Dinosauria in the United States National Museum, with special reference to the genera Antrodemus (Allosaurus) and Ceratosaurus. Bulletin of the United States National Museum 110: 1-154. Smithsonian Institution. doi:10.5479/si.03629236.110.i

    Definitive redescription of the holotype after the 1898-1899 USNM transfer; corrects Marsh's restoration errors and rejects Cope's referral to Megalosaurus.

    gilmore1920a
  4. Madsen, J. H.; Welles, S. P. (2000). Ceratosaurus (Dinosauria, Theropoda): A revised osteology. Utah Geological Survey Miscellaneous Publication 00-2 1-80. Utah Geological Survey.

    Modern osteological revision; names two additional Morrison species (C. dentisulcatus and C. magnicornis) and reassigns several Labrosaurus species, placing Labrosaurus in synonymy with Allosaurus.

    madsen2000a
  5. Glut, D. F. (1997). Ceratosaurus. Dinosaurs: The Encyclopedia 266-270. McFarland & Company. glut1997a
  6. Mateus, O.; Antunes, M. T. (2000). Ceratosaurus (Dinosauria: Theropoda) in the Late Jurassic of Portugal. 31st International Geological Congress.

    Abstract volume, Rio de Janeiro.

    mateus2000a
  7. Paul, G. S. (2016). The Princeton Field Guide to Dinosaurs (2nd ed.). 84. Princeton University Press. paul2016a
  8. Foster, J. (2020). Jurassic West: The Dinosaurs of the Morrison Formation and Their World. 217-219. Indiana University Press, Bloomington. foster2020a
  9. Sombathy, R.; O'Connor, P. M.; D'Emic, M. D. (2025). Osteohistology of the unusually fast-growing theropod dinosaur Ceratosaurus. Journal of Anatomy 247(3-4): 765-789. doi:10.1111/joa.14186 sombathy2025a
  10. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Theropods. Princeton University Press.

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

    jones2026c
  11. Hendrickx, C.; Bell, P. R.; Pittman, M.; Milner, A. R. C.; Cuesta, E.; O'Connor, J.; Loewen, M.; Currie, P. J.; Mateus, O.; Kaye, T. G.; Delcourt, R. (2022). Morphology and distribution of scales, dermal ossifications, and other non-feather integumentary structures in non-avialan theropod dinosaurs. Biological Reviews 97(3): 960-1004. doi:10.1111/brv.12829

    Documents the mosaic and sagittate dorsal-midline osteoderms on the neck and tail.

    hendrickx2022a
  12. Cope, E. D. (1892). On the skull of the dinosaurian Lælaps incrassatus Cope. Proceedings of the American Philosophical Society 30(138): 240-245. cope1892b