Open Paleo

Stegosaurus

Marsh, 1877 STEG-o-SAWR-us /ˌstɛɡəˈsɔːrəs/

From Greek stegos (roof) and sauros (lizard); meaning "roof lizard", in reference to the parasagittal rows of large dermal plates that Marsh initially interpreted as forming a roof-like carapace over the back of the animal.

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

Stegosaurus is the type genus of Stegosauridae and one of the most readily recognized dinosaurs, characterized by two parasagittal rows of large, erect dermal plates running from the cervicodorsal junction to near the tail tip and by four long tail spines (the "thagomizer") at the distal end of the tail. Marsh erected the genus and the order Stegosauria in 1877 on a partial skeleton from the Morrison Formation of Colorado, originally naming S. armatus as the type species. C. W. Gilmore's 1914 monograph on USNM 4934 (Felch Quarry No. 1, Garden Park, Colorado) supplied the first detailed osteology of the genus and resolved decades of argument over the plate arrangement, demonstrating from articulated evidence that the plates of the two rows alternate rather than pair. Because Marsh's S. armatus material is too fragmentary to anchor the genus, ICZN Opinion 2320 (2013) set aside all prior type-species fixations under plenary power and designated S. stenops Marsh, 1887, with USNM 4934 as its holotype, as the new type species — the form on which most of our modern picture of the genus rests. Besides the type species, S. ungulatus (Marsh, 1879) is also widely recognized as valid; other named forms are subsumed in Stegosaurus (S. duplex as a junior synonym of S. ungulatus, and Diracodon laticeps), while the synonymies of Hesperosaurus and Wuerhosaurus proposed by Maidment and colleagues (2008) remain contested in subsequent literature and are not accepted.

Diagnosis

  1. Skull comparatively very small with a brain cavity proportionally among the smallest of any large terrestrial vertebrate.
  2. Sacrum with an enormously enlarged neural canal forming a chamber many times the cranial capacity, fully roofed over by bone.
  3. Two parasagittal rows of erect, flattened, kite-shaped dermal plates extending from the cervicodorsal junction to near the tail tip; plates of opposite rows alternating rather than paired.
  4. Tail bearing four large dermal spines arranged in two pairs near the distal end (thagomizer); roughly 20-22 dermal plates total.
  5. Pes tetradactyl with digit IV reduced to a vestigial metatarsal; digit V absent.
  6. Tibia distinctive in having the greatest diameter of both ends lying approximately in the same plane.
  7. Postzygapophyses on the posterior cervical vertebrae elongate posteriorly, overhanging the back of the centrum.
  8. Supra-acetabular process of the ilium diverging at approximately 90 degrees from the anterior process.

Species (2)

Stegosaurus stenops Marsh, 1887

Type species

From Greek stenos (narrow) and ops (face); "narrow face", referring to the relatively narrow rostrum compared with other Stegosaurus material recognized at the time of Marsh's 1887 description.

Holotype
USNM 4934 , National Museum of Natural History, Smithsonian Institution
Material
Articulated and largely complete skeleton with skull, lower jaws, full presacral and sacral columns, 22 caudal vertebrae, both pectoral and pelvic girdles, fore- and hindlimbs, 17 dermal plates, one dermal spine, and numerous dermal ossicles.
Horizon
Morrison Formation, Kimmeridgian–Tithonian, Late Jurassic , 154.8–143.1 million years ago
Locality
Felch Quarry 1, Garden Park, Colorado, United States

Stegosaurus ungulatus Marsh, 1879

From Latin 'ungulatus' meaning 'hoofed', in reference to the hoof-like unguals of the type specimen.

Syntypes
YPM 1853, YPM 1858 , Yale Peabody Museum of Natural History
Material
Partial skull, several vertebrae, an ischium, partial limbs, several dermal plates, and four tail spikes (thagomizers).
Notes
Marsh (1879) named the species without designating a type, and Gilmore (1914) calls YPM 1853, from Quarry 12, and YPM 1858, from Quarry 11, its cotypes. Galton (2010) calls them syntypes and YPM 1853 "The paralectotype", but no work read designates a lectotype. YPM 1858 is also the type of Stegosaurus duplex.
Horizon
Morrison Formation, Kimmeridgian–Tithonian, Late Jurassic , 154.8–143.1 million years ago
Locality
Quarries 11 and 12, Como Bluff, Wyoming, United States
Diagnosis
  1. Longer hind limb (femur) and hip bones than in S. stenops
  2. Plates proportionately smaller and more pointed, with wide bases and narrow tips, rather than the large broad plates of S. stenops
  3. A pair of small, flattened, spine-like plates positioned just before the tail spikes, mirrored in shape and arranged in pairs
  4. Sacral centra broad and rounded, lacking the ventral keel present in the sacrals of S. stenops
  5. Spinous processes of the sacral vertebrae taller than in S. stenops

Synonyms

  • Stegosaurus duplex junior subjective

    Type specimen (YPM 1858) is one of the cotypes upon which Marsh founded S. ungulatus (Gilmore, 1914); now regarded as synonymous with S. ungulatus.

Synonyms of the genus

Name Type Reason
Diracodon laticeps junior subjective Erected by Marsh (1881) on two imperfect maxillae from Como Bluff, Wyoming (YPM 1885). Gilmore (1914) found the genus to rest entirely on teeth and maxillary characters that agree with Stegosaurus, and the carpal and tarsal characters Marsh added later to be features of immaturity. The caudal vertebrae and spines Marsh figured under the name in 1887 were referred to S. stenops, but Gilmore expressly excluded the 1881 name from that species synonymy, so the binomial attaches to the genus rather than to any one species.

Notable specimens

  • “Sophie”

    NHMUK PV R 36730 Natural History Museum Found 2003 by Bob Simon most complete

    The best preserved Stegosaurus specimen, 85 percent intact with 360 bones. A young adult of undetermined sex, 5.8 meters long and 2.9 meters tall, from a quarry near Shell, Wyoming; it went on display in December 2014 and was scientifically described in 2015.

    Maidment et al. (2015)

ICZN cases

References

  1. Galton, P. M. (2010). Species of plated dinosaur Stegosaurus (Morrison Formation, Late Jurassic) of western USA: new type species designation needed. Swiss Journal of Geosciences 103(2): 187-198. Springer Science and Business Media LLC. doi:10.1007/s00015-010-0022-4

    Gives Stegosaurus ungulatus as "based upon two syntypes", YPM 1853 from Quarry 12 and YPM 1858 from Quarry 11.

    galton2010a
  2. Maidment, S. C. R.; Brassey, C.; Barrett, P. M. (2015). The postcranial skeleton of an exceptionally complete individual of the plated dinosaur Stegosaurus stenops (Dinosauria: Thyreophora) from the Upper Jurassic Morrison Formation of Wyoming, U.S.A. PLOS ONE 10(10): e0138352. Public Library of Science (PLoS). doi:10.1371/journal.pone.0138352 maidment2015a
  3. Marsh, O. C. (1877). A new order of extinct Reptilia (Stegosauria) from the Jurassic of the Rocky Mountains. American Journal of Science s3-14(84): 513-514. doi:10.2475/ajs.s3-14.84.513

    Erects the genus Stegosaurus and the order Stegosauria on a partial Morrison-Formation skeleton; original type species S. armatus, later superseded by S. stenops.

    marsh1877a
  4. Marsh, O. C. (1887). Principal characters of American Jurassic dinosaurs, part IX. The skull and dermal armour of Stegosaurus. American Journal of Science s3-34(203): 413-417. doi:10.2475/ajs.s3-34.203.413

    Erects Stegosaurus stenops on USNM 4934, later designated the type species of Stegosaurus under ICZN Opinion 2320.

    marsh1887a
  5. Marsh, O. C. (1879). Notice of new Jurassic reptiles. American Journal of Science s3-18(108): 501-505. American Journal of Science (AJS). doi:10.2475/ajs.s3-18.108.501

    Erects Stegosaurus ungulatus from the Morrison Formation of Como Bluff, Wyoming, without numbering or designating a type.

    marsh1879a
  6. Gilmore, C. W. (1914). Osteology of the armored Dinosauria in the United States National Museum, with special reference to the genus Stegosaurus. United States National Museum Bulletin 89: 1-136.

    Foundational monograph on USNM 4934 (the future neotype- equivalent holotype of S. stenops). Establishes the alternating plate arrangement and supplies the first detailed osteology of the genus.

    gilmore1914b
  7. Maidment, S. C. R.; Norman, D. B.; Barrett, P. M.; Upchurch, P. (2008). Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia). Journal of Systematic Palaeontology 6(4): 367-407. Informa UK Limited. doi:10.1017/S1477201908002459

    Alpha-level revision of Stegosauria; sinks Hesperosaurus and Wuerhosaurus into Stegosaurus (as S. mjosi and S. homheni). Both synonymies are contested in subsequent literature.

    maidment2008a
  8. International Commission on Zoological Nomenclature (2013). Opinion 2320 (Case 3536). Stegosaurus Marsh, 1877 (Dinosauria, Ornithischia): type species replaced with Stegosaurus stenops Marsh, 1887. Bulletin of Zoological Nomenclature 70(2): 129-130. International Trust for Zoological Nomenclature.

    Resolves Case 3536 (Galton, 2011). Sets aside all prior type-species fixations under plenary power and designates S. stenops Marsh, 1887 (holotype USNM 4934) as the new type species. Vote 22-3.

    iczn2013a
  9. Paul, G. S. (2024). The Princeton Field Guide to Dinosaurs (3rd ed.). Princeton University Press.

    Source of the appearance features.

    paul2024a
  10. Marsh, O. C. (1881). Principal characters of American Jurassic dinosaurs, Part V. American Journal of Science 21: 417-423.

    Erected Diracodon laticeps, later synonymized with Stegosaurus.

    marsh1881b
  11. Galton, P. M. (2011). Case 3536. Stegosaurus Marsh, 1877 (Dinosauria, Ornithischia): proposed replacement of the type species with Stegosaurus stenops Marsh, 1887. Bulletin of Zoological Nomenclature 68(2): 127-133. doi:10.21805/bzn.v68i2.a14 galton2011a